                 FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,                   No. 09-50029
                Plaintiff-Appellee,
               v.                             D.C. No.
                                          3:01-cr-03177-W-2
MARK STEPHEN FORRESTER,
                                              OPINION
             Defendant-Appellant.
                                      
       Appeal from the United States District Court
         for the Southern District of California
       Thomas J. Whelan, District Judge, Presiding

                Argued and Submitted
         November 3, 2009—Pasadena, California

                   Filed January 5, 2010

  Before: Cynthia Holcomb Hall, Thomas G. Nelson and
           Milan D. Smith, Jr., Circuit Judges.

           Opinion by Judge Milan D. Smith, Jr.




                            303
308             UNITED STATES v. FORRESTER




                       COUNSEL

Benjamin L. Coleman and Ethan A. Baloch, Coleman &
Baloch, LLP, Attorneys for defendant-appellant Mark Ste-
phen Forrester.

Karen P. Hewitt, Bruce R. Castetter, Todd W. Robinson, and
Stewart M. Young, Attorneys for plaintiff-appellee United
States of America.
                  UNITED STATES v. FORRESTER                309
                          OPINION

MILAN D. SMITH, JR., Circuit Judge:

   Defendant-Appellant Mark Stephen Forrester (Forrester)
appeals his conviction and sentence for conspiracy to manu-
facture and distribute ecstasy in violation of 21 U.S.C. §§ 846
and 841(a)(1). Forrester and his codefendants operated a large
ecstasy laboratory that was under surveillance for over a year
before being closed by law enforcement authorities. Forrester
represented himself at trial, and was convicted and sentenced
to 30 years in prison. We previously remanded Forrester’s
case based on our finding that Forrester unintelligently
waived his right to counsel. On remand, Forrester pleaded
guilty, and was again sentenced to 30 years. He raises five
issues on appeal. First, he claims that the district court erred
by failing to allow him to argue that ecstasy should be catego-
rized as a Schedule III, rather than a Schedule I, controlled
substance, and that 21 U.S.C. § 841(b) is unconstitutional.
Second, he asserts that he has a present right to accept the
government’s original plea offer—which he originally
rejected—because he had been misadvised by the district
court concerning his maximum sentence exposure. Third, For-
rester alleges that his conspiracy indictment was unconstitu-
tionally vague. Fourth, he argues that the district court erred
in denying his motion to suppress all fruits of the wiretap.
Finally, he claims that the district court erred in sentencing
him to 30 years in prison.

  We affirm Forrester’s conviction, but vacate his sentence,
and remand for further proceedings consistent with this opin-
ion.

         FACTS, PRIOR PROCEEDINGS, AND
                  JURISDICTION

   Law enforcement authorities conducted a lengthy investiga-
tion into an elaborate conspiracy to manufacture ecstasy.
310               UNITED STATES v. FORRESTER
Investigators tracked the conspiracy for over a year using an
array of surveillance techniques. They traced chemical pur-
chases, used confidential informants to infiltrate the opera-
tion, followed Forrester to Stockholm where he met with
chemists, and discovered a clandestine laboratory in Escon-
dido, California. Agents raided the lab and seized large vol-
umes of ecstasy and precursor chemicals.

   In October 2001, Forrester and his codefendants were
charged with conspiracy to manufacture and distribute
ecstasy. On October 23, 2002, the district court held a Faretta
hearing to determine whether Forrester was competent to rep-
resent himself. The judge found that he was but, during the
hearing, the district judge misinformed Forrester that he was
facing a sentence of 10-years-to-life, when he was actually
facing a sentence of 0-to-20 years. Forrester represented him-
self from that point in the proceedings until his initial appeal.

   On July 3, 2003, the government approached Forrester and
his codefendant Dennis Alba (Alba) with a deal. They
informed Forrester and Alba that if they did not both plead
guilty that same day, the government would file an enhance-
ment pursuant to 21 U.S.C. § 851 requesting that Forrester’s
maximum sentence be increased from 20 to 30 years. For-
rester and Alba both declined the offer and, on July 18, 2003,
a jury found Forrester guilty. He was sentenced to 30 years on
May 26, 2003. Forrester appealed on May 31, 2003. We
found that Forrester had unknowingly and unintelligently
waived his right to counsel because the district judge misin-
formed him regarding his maximum sentence, United States
v. Forrester, 512 F.3d 500, 506-09 (9th Cir. 2008) (Forrester
I), and remanded the case to the district court. On remand,
Forrester entered a conditional guilty plea, and was sentenced
again to 30 years. He now appeals for the second time.

   We have jurisdiction under 28 U.S.C. § 1291 and 18 U.S.C.
§ 3742.
                  UNITED STATES v. FORRESTER                311
                STANDARDS OF REVIEW

   In addressing Forrester’s first claim regarding the classifi-
cation of ecstasy as a Schedule I substance, we review de
novo the district court’s construction or interpretation of a
statute. See Beeman v. TDI Managed Care Servs., Inc., 449
F.3d 1035, 1038 (9th Cir. 2006). The district court’s decision
to preclude a defendant’s proffered defense is also reviewed
de novo. See United States v. Batterjee, 361 F.3d 1210, 1216
(9th Cir. 2004).

  Forrester next argues that his failure to accept the plea was
involuntary. The voluntariness of a guilty plea is subject to de
novo review. See United States v. Gaither, 245 F.3d 1064,
1068 (9th Cir. 2001).

  Forrester also contests the sufficiency of the conspiracy
indictment, which we review de novo. United States v. Ber-
ger, 473 F.3d 1080, 1097 (9th Cir. 2007).

   We next address a number of issues with regard to the
wiretap application. We review de novo the district court’s
interpretation of the wiretap statute. United States v. Luong,
471 F.3d 1107, 1109 (9th Cir. 2006). A bifurcated standard of
review applies to wiretap necessity findings. First, we review
de novo whether a wiretap application is supported by a full
and complete statement of the facts in compliance with 18
U.S.C. § 2518(1)(c). United States v. Rivera, 527 F.3d 891,
898 (9th Cir. 2008). If a wiretap is adequately supported, then
we review the district court’s necessity finding for abuse of
discretion. United States v. Lynch, 437 F.3d 902, 912 (9th Cir.
2006).

   Finally, Forrester raises three sentencing issues. We review
ex post facto challenges to sentencing decisions de novo.
United States v. Ortland, 109 F.3d 539, 543 (9th Cir. 1997).
Similarly, we review de novo whether the district court failed
to make sufficient findings. United States v. Carter, 219 F.3d
312                  UNITED STATES v. FORRESTER
863, 866 (9th Cir. 2000). Whether the method used by the dis-
trict court to approximate the quantity of drugs was proper
under the Guidelines is reviewed de novo, and factual find-
ings related to the capability of a drug operation are reviewed
for clear error. United States v. Chase, 499 F.3d 1061, 1068
(9th Cir. 2007).

                            DISCUSSION

   Forrester appeals his conviction and sentence. First, he
argues that ecstasy should be classified as a Schedule III sub-
stance, and that his maximum sentence must be determined by
a jury. Second, he asserts that misinformation regarding his
maximum sentence rendered his rejection of a plea deal unin-
telligent. Third, he claims that his conspiracy indictment was
unconstitutionally vague. Fourth, he alleges that the district
court erred in denying his motion to suppress all fruits of the
wiretap. Finally, he claims that his sentence was improper.

I.       Controlled Substance Scheduling

   [1] The Controlled Substances Act (CSA), 21 U.S.C. § 801
et seq., establishes five categories or “schedules” of controlled
substances. Ecstasy has been classified as a Schedule I con-
trolled substance since March 23, 1988. See 53 Fed. Reg.
5156 (Final Rule dated Feb. 22, 1988—Schedules of Con-
trolled Substances; Scheduling of 3,4 Methylenedioxy-
methamphetamine (MDMA) into Schedule I of the Controlled
Substances Act; Remand). Violations involving Schedule I
substances carry more severe penalties than those in Schedule
III because the drugs have a high potential for abuse and no
generally accepted medical benefits.1 21 U.S.C. § 812(b)(1).
Forrester claims that the district court erred by failing to allow
him to present a defense that ecstasy should be categorized as
     1
    The maximum Schedule I and III sentences for offenses committed by
a defendant with a prior drug conviction are 30 years and 10 years, respec-
tively. See §§ 841(b)(1)(C), (D).
                     UNITED STATES v. FORRESTER                        313
Schedule III rather than as Schedule I, which defense, had it
been allowed, would have subjected him to a lower maximum
penalty, as set forth in 21 U.S.C. § 841(b)(1)(D). Alterna-
tively, he argues that § 841(b) violates the Fifth and Sixth
Amendments because it allows a maximum sentence to be
determined by a fact not found by the jury.

  A.    Collateral Attack on a Scheduling Order

   [2] The Attorney General (AG) has designated ecstasy as
a Schedule I controlled substance under the CSA.2 The CSA
allows the AG to schedule a substance on a temporary basis
when doing so is “necessary to avoid an imminent hazard to
the public safety.” 21 U.S.C. § 811(h).3

   [3] Forrester argues that the Schedule III definition more
accurately describes ecstasy than does the one in Schedule I,
and that “the scheduling of ecstasy has been questioned by the
medical community.” Forrester further argues that denying
him the opportunity to argue that ecstasy should be designated
a Schedule III controlled substance violates Touby v. United
States, 500 U.S. 160 (1991). Specifically, Forrester believes
that he has a right to collaterally attack the substance of the
scheduling order because Congress has not explicitly fore-
closed such review. This is an issue of first impression in this
circuit.
  2
     Congress delegated the authority to schedule drugs to the AG, 21
U.S.C. § 811(h) and the AG, in turn, has delegated the authority to update
the CSA schedules to the Drug Enforcement Agency (DEA). 28 C.F.R.
§ 0.100. However, the legitimacy of this delegation is not at issue here;
accordingly, for purposes of this opinion, we attribute scheduling deci-
sions to the AG.
   3
     This allows the AG to bypass, for a limited time, the lengthy procedure
required for permanent scheduling and thus enables the government to
respond more quickly to dangerous new drugs. Temporary scheduling
orders remain valid for one year. Section 811(h)(6) provides that a tempo-
rary order is not subject to “judicial review.” Id.
314               UNITED STATES v. FORRESTER
   In Touby, the petitioners were convicted of conspiring to
manufacture “Euphoria,” a designer drug that was temporarily
placed under Schedule I. 500 U.S. at 162. The primary ques-
tion in Touby was whether the AG’s power to temporarily
schedule a substance violated the non-delegation doctrine. Id.
at 164-67. The Court also considered whether the temporary
scheduling statute was unconstitutional because it bars judi-
cial review. Id. at 168-69. The Court held that (1) direct, pre-
enforcement review of a permanent scheduling order is
plainly authorized by 21 U.S.C. § 877 and that petitioners
wishing to challenge the order can do so when the temporary
order becomes permanent, (2) the AG’s compliance with his
delegated duties may always be challenged by individuals fac-
ing criminal charges, whether they are temporary or perma-
nent, and (3) substantive, collateral attacks on temporary
scheduling orders may be brought by criminal defendants
whose sentences will be affected by the order. Id. at 160.

   The concurring opinion in Touby emphasized that “the
opportunity of a defendant to challenge the substance of a
temporary scheduling order in the course of a criminal prose-
cution is essential to the result in this case” and that Congress
“did not intend to foreclose review in the enforcement con-
text.” Id. at 169-70. The concurring minority was concerned
that temporary scheduling orders, which have not been fully
vetted by the AG or passed all of the necessary procedural
requirements, were going to have a severe impact on criminal
defendants who were sentenced pursuant to the orders. In
effect, the opinion permitted a concurrent vetting by the
courts to ensure that such temporary orders were not
improper. We construe Touby’s holding to be limited to tem-
porary orders because permanent orders are thoroughly vetted
and allow for direct attacks through 21 U.S.C. § 877.

  The Eleventh Circuit, the only circuit to have previously
addressed this issue to date, came to the same conclusion.
United States v. Carlson, 87 F.3d 440 (11th Cir. 1996). Carl-
son, like Forrester, attempted to substantively challenge the
                  UNITED STATES v. FORRESTER                 315
AG’s ruling that ecstasy is a Schedule I controlled substance.
Id. at 446. The Eleventh Circuit held that a defendant cannot
“make a collateral attack on a final regulatory decision in a
criminal case.” Id. It gave two reasons: “[f]irst, the decision
to schedule a substance like [ecstasy] is a complex matter, . . .
[and] [s]econd, and more importantly, the agency itself is not
a party in the case; hence it has no opportunity to defend its
scheduling order.” Id. Additionally, to allow all criminal
defendants to collaterally attack a permanent scheduling order
based on their view that a particular drug has been mis-
scheduled would potentially place a continuing, onerous bur-
den on district courts to constantly re-litigate the same issue.

  [4] Forrester argues that, in other situations, Congress has
been explicit about not permitting collateral attacks at trial.
For example, 8 U.S.C. § 1189(a)(8) states:

    If a designation under this subsection has become
    effective under paragraph (2)(B) a defendant in a
    criminal action or an alien in a removal proceeding
    shall not be permitted to raise any question concern-
    ing the validity of the issuance of such designation
    as a defense or an objection at any trial or hearing.

Section 1326(d) contains a similar provision in the deporta-
tion context. However, the evidence that Congress has, at
times, taken a more proactive stance toward controlling col-
lateral challenges is not sufficient to overcome our reading of
Touby, and the persuasive reasoning of our sister circuit, to
the effect that collateral attacks are not permitted in criminal
cases involving permanent scheduling orders.

   [5] We hold that substantive collateral attacks on perma-
nent scheduling orders are impermissible in criminal cases
where defendants’ sentences will be determined by those
scheduling orders. Accordingly, we conclude that the district
court did not err in denying Forrester’s motion for an eviden-
tiary hearing on the issue.
316                UNITED STATES v. FORRESTER
  B.   Constitutionality of 21 U.S.C. § 841(b)

   Forrester also argues that 21 U.S.C. § 841(b)(1)(C) violates
the Fifth and Sixth Amendments, as construed in Apprendi v.
New Jersey, 530 U.S. 466 (2000), and United States v. Buck-
land, 289 F.3d 558 (9th Cir. 2002), because it allows his max-
imum sentence to be determined by a fact not found by the
jury beyond a reasonable doubt.

   [6] The Supreme Court held in Apprendi that “[o]ther than
the fact of a prior conviction, any fact that increases the pen-
alty for a crime beyond the prescribed statutory maximum
must be submitted to a jury, and proved beyond a reasonable
doubt.” 530 U.S. at 490. In Buckland, the government con-
ceded that the district court had violated Apprendi when it,
rather than the jury, determined the quantity of drugs attribut-
able to the defendant. Buckland, 289 F.3d at 568. Forrester
contends that the question of whether ecstasy meets the defi-
nition of a Schedule I substance is a factual determination that
must be left to the jury.

   [7] In both Apprendi and Buckland, the judges made
improper findings of conduct (sale of a particular drug and
engaging in hate speech, respectively) by a preponderance of
the evidence. The respective courts held that those findings
should have been made by a jury beyond a reasonable doubt.
See Buckland, 289 F.3d at 563; Apprendi, 530 U.S. at 471.
However, both cases explicitly confirm Congress’s ability to
“ramp up the punishment for controlled substance offenders
based on the type and amount of illegal substance involved in
the crime.” Buckland, 289 F.3d at 568; see also Apprendi, 530
U.S. at 495 (recognizing Congress’s ability to choose “[t]he
degree of culpability . . . associate[d] with particular, factually
distinct conduct”). Therefore, under Buckland and Apprendi,
the relevant fact questions for the jury in this case would have
been what conduct Forrester engaged in (conspiracy to manu-
facture and distribute drugs) and what type of drug was
involved in the conspiracy (ecstasy). Here, those are issues of
                     UNITED STATES v. FORRESTER                        317
fact that would have been found by a jury had Forrester gone
to trial, instead of pleading guilty.4 In contrast, the question of
whether ecstasy is a drug that warrants greater restrictions and
punishment because of its highly undesirable qualities is one
that has been properly delegated to the legislative branch. In
other words, it is within the realm of Congress’s power to
“ramp up the punishment” for ecstasy. Buckland, 289 F.3d at
568. The AG, with the power delegated by Congress,5 chose
to do so by categorizing it as Schedule I rather than as Sched-
ule III. In the same way that elements of a crime are deter-
mined by Congress, so are the classifications of certain illegal
drugs. Determining which offenses are worthy of greater pun-
ishments is a legislative prerogative. This policy judgment
cannot properly be construed as a “fact that increases the pen-
alty for a crime” within the meaning of Apprendi. 530 U.S. at
490.

II.   Rejected Plea Offer

   On October 23, 2002, Forrester waived his right to counsel
under Faretta v. California, 422 U.S. 806 (1975) (the Faretta
hearing). However, during the Faretta hearing colloquy, the
district court incorrectly advised Forrester that he faced 10
years-to-life in prison, whereas he actually faced zero-to-20
years in prison. Forrester I, 512 F.3d at 507. The government
did not correct the court’s erroneous advice.

   On July 3, 2003 (five days before trial), the government
extended a plea offer to Forrester and Alba. The government
told Forrester that if both he and Alba accepted the “package
deal,” Forrester could limit his exposure to 20 years. The gov-
  4
     Forrester pleaded guilty and thus waived his right to a jury trial. His
guilty plea thus stands in the place of a jury’s findings. See United States
v. Banuelos, 322 F.3d 700, 709 n.3 (9th Cir. 2003) (Tallman, J., dissenting
in part) (citing United States v. Sanchez, 269 F.3d 1250, 1272 n.2 (11th
Cir. 2001)).
   5
     See supra note 2.
318                UNITED STATES v. FORRESTER
ernment stated that if the plea offer was not accepted by 2:00
pm that same day, it would file a sentence enhancement pur-
suant to 21 U.S.C. § 851. The offer was not accepted by either
Forrester or Alba, and the government filed the § 851
enhancement, thereby enhancing Forrester’s maximum pen-
alty from 20 to 30 years. See 21 U.S.C. § 841(b)(1)(C).

   The case proceeded to trial and Forrester was convicted,
and sentenced to the maximum of 30 years. We reversed,
finding a defective waiver of counsel due to the district
court’s erroneous sentencing advisement during the Faretta
hearing. Forrester I, 512 F.3d at 505-09. Following remand,
Forrester filed a motion requesting that the district court strike
the § 851 enhancement and allow him to plead guilty without
the enhancement because he had been misadvised of the
potential penalties at the Faretta hearing. The district court
denied the motion, stating:

      Well, the government has the right to file anything
      they think, any conduct or convictions they think
      they can prove. With regard to misadvising him of
      the maximum penalty, you are absolutely correct I
      did misadvise him. No question about that.

      ...

      In any event, I don’t think there is anything inappro-
      priate for the government having filed that 851 alle-
      gation. I understand your honor [sic] position, but
      your request that I have it stricken or dismissed is
      denied.

Forrester then pleaded guilty and was sentenced (again) to the
30-year maximum. Forrester alleges that the district court
erred by failing to dismiss the § 851 sentence enhancement
due to its prior sentencing miscalculation, thereby depriving
him of the opportunity to make a knowing and intelligent
                  UNITED STATES v. FORRESTER                  319
decision to accept an earlier plea offer that did not include the
enhancement.

   [8] Federal Rule of Criminal Procedure 11(b) states that the
court must hold a hearing and inform a defendant of, and
determine that he understands, “any maximum possible pen-
alty, including imprisonment, fine, and term of supervised
release” and “any mandatory minimum penalty,” before it
accepts his guilty plea (the plea hearing). FED. R. CRIM. P.
11(b)(1)(H) & (I). A failure to ensure that a defendant under-
stands his range of exposure may violate the requirement that
a guilty plea be “knowing and voluntary.” See, e.g., Tanner
v. McDaniel, 493 F.3d 1135, 1146 (9th Cir. 2007) (holding
that guilty plea is voluntary and knowing only if defendant
understands the range of allowable punishment that will result
from his plea). Forrester’s case differs from the standard situ-
ation where pleas are found involuntary due to misinforma-
tion about the potential sentence in two ways: (1) Forrester
rejected the plea offered to him, and (2) the court misin-
formed him of his exposure during a Faretta hearing rather
than during a plea hearing.

   [9] “[T]here is no constitutional right to plea bargain.”
Weatherford v. Bursey, 429 U.S. 545, 561 (1977). Nonethe-
less, defendants who plead guilty are given the protection of
the “voluntary and intelligent” requirement because, in plead-
ing guilty, they are relinquishing fundamental constitutional
rights. See FED. R. CRIM. P. 11(b) (detailing defendant’s right
to plead not guilty, to a jury trial, to have counsel, to confront
witnesses, and to present evidence). However, the voluntary
and intelligent requirement has never been extended to rejec-
tions of plea offers. When a defendant turns down a guilty
plea, he is giving up only the opportunity to limit his exposure
to the terms of that plea.

  Forrester argues that, once a plea offer has been made, a
defendant has a right to be accurately informed about his
potential exposure before deciding to reject it. He relies on
320               UNITED STATES v. FORRESTER
Nunes v. Mueller, a habeas case in which an attorney misin-
formed the defendant that he had received a plea offer for 22
years as opposed to 11 years. 350 F.3d 1045 (9th Cir. 2003).
In Nunes, we suggested that the right to make an informed
decision about a plea is a corollary to the right to voluntarily
and intelligently plead guilty. Id. at 1053 (“The right that
Nunes claims he lost was not the right to a fair trial or the
right to a plea bargain, but the right to participate in the deci-
sion as to, and to decide, his own fate—a right also clearly
found in Supreme Court law.”). In that case, we ordered the
reinstatement of Nunes’ original plea offer, rather than the
more common remedy of a new trial, in order to “put the
defendant back in the position he would have been in if the
Sixth Amendment violation never occurred.” Id. at 1057
(internal quotation marks omitted).

   [10] Nunes was based on the well-founded constitutional
right to effective assistance of counsel. Id. at 1051-1054. For
Nunes to apply here, we would have to find that Forrester suf-
fered a similar unconstitutional deprivation of rights that
tainted his rejection of the plea offer. We decline to do so on
these facts. Though a defendant may have a right to voluntar-
ily and intelligently reject a plea offer, we need not reach that
question in this case because any error was harmless. See
Bains v. Cambra, 204 F.3d 964, 971 n.3 (9th Cir. 2000) (recit-
ing Chapman “harmless beyond a reasonable doubt” standard
for constitutional trial type errors).

   First, Forrester was offered a “package deal” with Alba.
Because Alba rejected the deal, Forrester could not unilater-
ally have accepted it even if he had been aware of his actual
potential sentence. Indeed, Alba had no incentive to accept
the plea, as the threatened enhancement did not affect his
exposure because he already faced life in prison on a continu-
ing criminal enterprise count.

  [11] Second, Forrester’s maximum and minimum possible
sentences were overstated. Forrester was offered a 20-year
                     UNITED STATES v. FORRESTER                        321
cap on his sentence when he thought he faced 10-to-life if he
went to trial. In rejecting the offer to cap his exposure at 20
years, he risked receiving what he thought was a life sentence
for the potential benefit of being acquitted. He now claims
that, had he known that he actually faced a potential sentence
of 0-to-30 years (with the enhancement), he would have fore-
gone risking the 30-year maximum and accepted the deal to
cap his exposure at 20 years. In other words, he says he was
willing to risk receiving 10-to-life for the possibility of
acquittal, but would not have been willing to take his chances
at 0-to-30. We find this argument counterintuitive. Though it
is certainly possible that a misinformed defendant may reject
a plea that he otherwise would have taken, that was undoubt-
edly not the case here. Cf. United States v. Stubbs, 279 F.3d
402, 411 (6th Cir. 2002) (“When the maximum possible sen-
tence is overstated, the defendant might well be influenced to
accept a plea agreement he would otherwise reject.” (empha-
sis added) (internal quotation marks omitted)).6 Therefore, the
district court’s denial of the motion to strike the enhancement
was proper.

III.    Sufficiency of the conspiracy indictment

   Forrester alleges that his indictment for conspiracy was
insufficient. The second superseding indictment at issue
reads:

       Beginning at a date unknown to the grand jury and
       continuing up to and including October 18, 2001,
       within the Southern District of California, and else-
       where, [Forrester and 18 other named defendants],
  6
    In Forrester I, we rejected a similar argument that the district court’s
overstatement made Forrester less likely to waive counsel. 512 F.3d at
507-08. We emphasized in that context, however, that harmless error
review does not apply to Faretta waivers. Id. at 508. By contrast, errors
relating to plea hearings are subject to harmless error review. See United
States v. Minore, 292 F.3d 1109, 1120 (9th Cir. 2002), cert. denied, 537
U.S. 1146 (2003).
322                UNITED STATES v. FORRESTER
      all charged elsewhere, did knowingly and intention-
      ally conspire together and with each other and with
      other persons known and unknown to the grand jury
      to manufacture and distribute a controlled substance,
      to wit, 3,4 Methylenedioxyamphetamine (“MDA”),
      commonly known as “ecstasy”, a Schedule I Con-
      trolled Substance, in violation of Title 21, United
      States Code, Sections 846 and 841(a)(1).

Forrester filed a motion to dismiss for deficiency, and the dis-
trict court denied the motion without explanation.

   [12] An indictment “must be a plain, concise and definite
written statement of the essential facts constituting the offense
charged.” FED. R. CRIM. P. 7(c)(1). “An indictment is suffi-
cient if it (1) contains the elements of the offense charged and
fairly informs a defendant of the charge against him which he
must defend and (2) enables him to plead an acquittal or con-
viction in bar of future prosecutions for the same offense.”
United States v. Lazarenko, 564 F.3d 1026, 1033 (9th Cir.
2009) (internal quotation marks omitted). “Generally, an
indictment is sufficient if it sets forth the elements of the
charged offense so as to ensure the right of the defendant not
to be placed in double jeopardy and to be informed of the
offense charged.” United States v. Rodriguez, 360 F.3d 949,
958 (9th Cir. 2004) (internal quotation marks omitted). With
respect to conspiracies, “[a]n indictment under 21 U.S.C.
§ 846 . . . is sufficient if it alleges: a conspiracy to distribute
drugs, the time during which the conspiracy was operative
and the statute allegedly violated, even if it fails to allege or
prove any specific overt act in furtherance of the conspiracy.”
United States v. Tavelman, 650 F.2d 1133, 1137 (9th Cir.
1981) (internal quotation marks omitted).

   [13] Forrester contends that the indictment is insufficient
because it fails to specify a beginning date for the conspiracy,
thereby possibly subjecting him to double jeopardy. However,
although an indictment cannot be completely open-ended, see
                  UNITED STATES v. FORRESTER                 323
United States v. Cecil, 608 F.2d 1294, 1296-97 (9th Cir.
1979), an indictment that specifies an end date is sufficient to
apprise defendants of the charges and enable them to prepare
a defense, see United States v. Rohrer, 708 F.2d 429, 435 n.7
(9th Cir. 1983) (holding that an indictment alleging that the
conspiracy extended until “at least” 1980 was sufficient).

   [14] In addition, uncertainty regarding a conspiracy’s
beginning and ending dates does not render an indictment
fatally defective so long as overt acts alleged in the indictment
adequately limit the time frame of the conspiracy. United
States. v. Laykin, 886 F.2d 1534, 1542 (9th Cir. 1989) (18
specific facts alleged in the indictment were sufficient to limit
the time frame). Here, the second superceding indictment
tracks the language of the conspiracy statute, identifies a loca-
tion and co-conspirators, and alleges the purpose of the con-
spiracy. It also alleged a semi-discrete time period (it gave an
end date but no beginning date) and certain overt acts. Taken
together, the indictment was sufficient to apprise Forrester of
the charges against him, enable him to prepare a defense, and
to avoid double jeopardy on the same charge. We thus con-
clude that the district court did not err in denying Forrester’s
motion to dismiss the indictment.

IV.   The Wiretap

   On February 5, 2001, the government submitted an initial
application for a 30-day wiretap order. The application con-
tained a 53-page affidavit by Special Agent Robert Aguirre,
and a separate 3-page affidavit (Exhibit C) that was filed
under seal. The district judge approved the wiretap on the
same day. Forrester challenges the wiretap on several
grounds. First, he claims that he was entitled to access the
redacted contents of Exhibit C. Second, he claims that the
wiretap application failed to comply with the “necessity”
requirement of the statute. Third, he claims that the wiretap
violated the Fourth Amendment.
324                UNITED STATES v. FORRESTER
  A.    Right to View the Redacted Affidavit

  Exhibit C provided information about a confidential infor-
mant referred to as “CS.” Federal Rule of Criminal Procedure
16 governs government disclosure of information, stating:

      Upon a defendant’s request, the government must
      permit the defendant to inspect and to copy or photo-
      graph books, papers, documents, data, photographs,
      tangible objects, buildings or places, or copies or
      portions of any of these items, if the item is within
      the government’s possession, custody, or control
      and:

          (i) the item is material to preparing the
          defense;

          (ii) the government intends to use the item
          in its case-in-chief at trial; or

          (iii) the item was obtained from or belongs
          to the defendant.

FED. R. CRIM. P. 16(a)(1)(E). In addition, 18 U.S.C. § 2518
states that the fruits of a wiretap may not be used in court
unless a copy of the court order and the wiretap application
are furnished to each party:

      The contents of any wire, oral, or electronic commu-
      nication intercepted pursuant to this chapter or evi-
      dence derived therefrom shall not be received in
      evidence or otherwise disclosed in any trial, hearing,
      or other proceeding . . . unless each party . . . has
      been furnished with a copy of the court order, and
      accompanying application, under which the intercep-
      tion was authorized or approved.

Id. § 2518(9).
                  UNITED STATES v. FORRESTER                 325
   [15] The district court denied Forrester’s motion for spe-
cific discovery of Exhibit C. It found that the items sought
were not discoverable under Rule 16 because they were not
material to the presentation of the defense. The question is
whether 18 U.S.C. § 2518, which mandates disclosure of the
wiretap application, allows the government to redact some
information in the application. This is a question of first
impression in our circuit, though one that has been addressed
by other courts.

   Forrester asks us to adopt the reasoning of the district court
in United States v. Arreguin, 277 F. Supp. 2d 1057 (E.D. Cal.
2003). That court held that, pursuant to 18 U.S.C. § 2518(9),
a defendant has a right to all wiretap application materials,
including unredacted copies of affidavits in support of the
application. It reasoned that 18 U.S.C. § 2518 “was enacted
to provide greater [privacy] protection than that mandated by
the Constitution under then-existing precedent,” id. at 1060
(citing Gelbard v. United States, 408 U.S. 41, 48 n.7 (1972)),
and noted that “[t]he statutory requirements for wiretap autho-
rization are far more burdensome than those mandated by the
Constitution,” id. at 1060-61. Similarly, the court noted that
18 U.S.C. § 2518(8)(b) provides that wiretap applications can
not be unsealed absent a showing of good cause and gives
judges discretion in determining what to disclose. Id. at 1061.
Section 2518(9), on the other hand, requires that each party
receive a copy of the wiretap application before evidence may
be received—it does not include any of the discretionary lan-
guage found in § 2518(8)(b). Id. The district court considered
this to be “a judgment by Congress that the good cause
requirement is satisfied where the government plans to use
evidence derived from a wiretap.” Id. at 1061-62. Under that
reasoning, the court required the government to disclose wire-
tap applications in their entirety before using the evidence
derived from the wiretaps. Id. at 1062-63; see also United
States v. Manuszak, 438 F. Supp. 613, 619, 625 (E.D. Pa.
1977) (“Unlike Section 2518(8)(d) . . . which gives the court
discretion to deny access to the order and application, Section
326                   UNITED STATES v. FORRESTER
2518(9) mandates that these items be made available to a
party facing any proceeding[.]” (internal quotation marks
omitted)).

   [16] We find the reasoning in United States v. Danovaro
more persuasive. 877 F.2d 583 (7th Cir. 1989). In that case,
the Seventh Circuit held that a defendant does not have a right
to redacted portions of a wiretap application if the govern-
ment is able (and willing) to defend the warrant without rely-
ing on the redacted information. Id. at 588. The court
determined that such a rule was consistent with 18 U.S.C.
§ 2518(9) because “[s]tatutes requiring disclosure, but silent
on the question of privilege, do not override customary privi-
leges.” Id. (citing Upjohn Co. v. United States, 449 U.S. 383,
397-98 (1981)). Furthermore, the privilege to withhold infor-
mation in order to protect informants is well-established. See
Roviaro v. United States, 353 U.S. 53, 59 (1957).7 The Dano-
varo court held that the information excised in that case,
which had been examined in camera, was not essential to sup-
port the warrant or to show that a wiretap was necessary. 877
F.2d at 588. Because the redacted portions were not neces-
sary, the Seventh Circuit declined to determine whether the
government can redact information (with in camera review)
when the information is essential to the validity of the war-
rant. Id. We adopt as the rule of this Circuit the Seventh Cir-
cuit’s narrow rule from Danovaro,8 but we also decline to
  7
     The Arreguin court, in contrast, held that the statutory disclosure
requirement of § 2518(9) always trumps the informant privilege set forth
in Roviaro. See Arreguin, 277 F. Supp. 2d at 1061.
   8
     At least two other district courts have also found Danovaro more per-
suasive than Arreguin. See United States v. Coles, No. 05-440, 2007 WL
2916510, at *2 (E.D. Pa. Oct. 4, 2007) (“The Arreguin court’s analysis has
the appeal of simplicity, as it confines its assessment to the statutory text
and draws its conclusions based on what it regards as clear Congressional
intent. We do not agree with the Eastern District of California, however,
that Congressional intent on this question is so self-evident. Moreover, we
are concerned that the Arreguin court and the Defendant, to the extent he
urges the adoption of its analysis, embraces a sort of formalistic approach
                      UNITED STATES v. FORRESTER                          327
determine whether the government can redact information
when that information is essential to the validity of the war-
rant.

  The preamble to Exhibit C states: “As noted in Exhibit B,
none of the information set forth in this supplemental plead-
ing is being submitted to establish either probable cause or
necessity for the requested wiretap.” The rest of the two-and-
a-half page document is redacted. Exhibit B explains that

     [d]ue to the nature of the CS’s cooperation with law
     enforcement officers and the risk to the safety of the
     CS if his/her identity is disclosed, I am submitting
     details regarding the CS’s background and knowl-
     edge in [Exhibit C]. For the purpose of establishing
     probable cause for the requested wire intercept, I am
     not submitting the facts and circumstances in Exhibit
     C; rather, I am providing the Court with the informa-
     tion in Exhibit C to substantiate my belief that the
     CS is a reliable source of information and, as
     addressed below, to show the limitations of the CS
     with respect to law enforcement’s ability to achieve
     the goals of this investigation without the requested
     wiretap authorization.

Because, as discussed below, the unredacted parts of the wire-
tap application were more than sufficient to establish neces-
sity, we find that the district court did not err in denying
Forrester’s motion for specific discovery.

to Title III that has been rejected by the Third Circuit.”); United States v.
Freeman, No. 06-205-03, 2008 WL 879966, at *2-3 (E.D. Pa. Mar. 31,
2008) (“Like the court in Coles, I find it unwise to rely solely on the tex-
tual peculiarities of Title III to conclude that Congress’s intent was that the
informer’s privilege not apply to disclosures pursuant to § 2518(9). Conse-
quently, I disagree with the reasoning and conclusion of Arreguin. More-
over, I find persuasive the reasoning of the . . . Seventh Circuit in
Danovaro . . . .”).
328               UNITED STATES v. FORRESTER
  B.   § 2518’s Necessity Requirement

   Under 18 U.S.C. § 2518(3)(c), a judge may authorize a
wiretap if the application demonstrates that “normal investi-
gative procedures have been tried and have failed or reason-
ably appear to be unlikely to succeed if tried or to be too
dangerous.” This “necessity requirement” is intended to
ensure that wiretapping is not resorted to in situations where
traditional investigative techniques would suffice to expose
the crime. United States v. Kahn, 415 U.S. 143, 153 n.12
(1974).

   The district court authorized the wiretap after finding that
it was necessary. The 72-page wiretap application extensively
detailed target subjects, the basis of information, the MDA
manufacturing process, the facts establishing probable cause,
and the inadequacy of traditional investigative techniques.
The latter section, spanning 20 pages, explained how the use
of confidential informants and undercover officers, physical
surveillance, pen registers, telephone rolls, search warrants,
interviews, grand jury subpoenas, and trash searches had
proven inadequate.

   [17] Forrester argues that the application did not provide a
full and complete statement regarding the government’s
investigatory techniques, and therefore failed to meet the
necessity requirement. In fact, the wiretap application con-
tained a full and complete statement of the facts. It described
in great detail the entire course of the investigation. It
described the target subjects and their backgrounds, the
numerous sources of information (DEA & Bureau of Narcot-
ics Enforcement agents, federal, state, and local drug task
force officers, and the Swedish National Criminal Investiga-
tive Department, among others), the MDA manufacturing
process, Forrester’s trips to Sweden to visit known ecstasy
manufacturers, specific chemical orders and shipments,
efforts to follow Forrester to Sweden and details of his activi-
ties there, and an extensive analysis of the pen register and
                   UNITED STATES v. FORRESTER                   329
toll information for the target telephone. To demonstrate that
traditional investigative techniques were insufficient, the affi-
davit described the use (and lack of success) of confidential
informants, undercover officers, physical surveillance (includ-
ing stationary cameras), pen registers, search warrants, inter-
views, and trash searches.

   Based on this full and complete statement, the district
court’s necessity finding was not an abuse of discretion. The
application carefully explains why traditional investigative
techniques would not have enabled officers to achieve the
goals of the investigation. For instance, it noted that one of
the confidential informants knew of a clandestine lab but
could not get the defendants to disclose its location. There
was also some evidence that the confidential informant (CI)
was receiving incorrect information, and as a drug buyer, the
CI was not privy to key information about the defendants’
operation. As another example, the application noted that the
use of physical (camera and video) surveillance had enabled
the government to identify some target subjects, confirm that
Forrester traveled to Sweden, and confirm a meeting between
Forrester and Alba. However, it could not establish the identi-
ties of all coconspirators or provide evidence of the purpose
and content of conspiratorial meetings. The application also
listed specific investigative goals not yet achieved through the
use of conventional techniques, including the identification of
all coconspirators of the target subjects, the manner in which
they were laundering the proceeds, and the locations where
they were manufacturing and distributing the ecstasy.

   Forrester’s reliance on United States v. Gonzalez, Inc., 412
F.3d 1102 (9th Cir. 2005), is misplaced. There, we found a
lack of necessity because the government’s investigation of a
particular office building in question was too limited. Id. at
1108. “This brief investigation included: five days of pen reg-
isters . . .; an equally brief use of trap-and-trace analysis of the
telephones; limited physical surveillance; and a preliminary
inquiry attempt to place an undercover agent . . . .” Id. The
330                UNITED STATES v. FORRESTER
investigation into Forrester and his codefendants, in compari-
son, went on for many months and was thorough and targeted.

   [18] The necessity requirement was intended to ensure that
wiretaps are not used as the initial step in a criminal investiga-
tion. United States v. Giordano, 416 U.S. 505, 515 (1974).
However, officials need not exhaust every conceivable inves-
tigative technique before obtaining a wiretap. United States v.
Commito, 918 F.2d 95, 98-99 (9th Cir. 1990); United States
v. Carneiro, 861 F.2d 1171, 1178 (9th Cir. 1988). Based on
these principles and the information contained in the wiretap
application, we find that the district court did not abuse its
discretion in finding that the wiretap was necessary, and deny-
ing the motion to suppress.

  C.    The Fourth Amendment Wiretap Claim

   Forrester argues that, even if the necessity requirement was
met, the application violated the Fourth Amendment standard
set forth in Berger v. New York, 388 U.S. 41 (1967) because
of a lack of exigent circumstances. In Berger, the Court held
that:

      [The wiretap statute] permits uncontested entry with-
      out any showing of exigent circumstances. Such a
      showing of exigency, in order to avoid notice would
      appear more important in eavesdropping, with its
      inherent dangers, than that required when conven-
      tional procedures of search and seizure are utilized.

Id. at 60. Berger did not create a bright-line exigency require-
ment. Rather, the Court was troubled that eavesdropping had
been authorized without requiring probable cause, without a
description of the conversations it sought to record, and with-
out a termination date. Id. at 59-60. Here, probable cause was
established, the wiretap was limited to one month, and the
application described the conversations and information that
it sought to “seize.”
                    UNITED STATES v. FORRESTER              331
   [19] Furthermore, the Supreme Court has routinely
acknowledged that § 2518 “prescribes the procedure for
securing judicial authority to intercept wire communications,”
Giordano, 416 U.S. at 507, and was enacted specifically to
“meet the constitutional requirements for electronic surveil-
lance enunciated by [the Supreme Court] in [Berger] and Katz
v. United States, 389 U.S. 347 (1967),” Mitchell v. Forsyth,
472 U.S. 511, 532 (1985) (internal quotations omitted).
Therefore, we conclude that because the wiretap application
met the standards set forth in § 2518, which do not require a
showing of exigent circumstances, the application did not vio-
late the Fourth Amendment.

V.     Sentencing

  A.      Temporary Amendment to the Ecstasy Act

   [20] The November 2000 sentencing manual provided that
one gram of MDA was the equivalent of 50 grams of mari-
juana. U.S.S.G. § 2D1.1 (2000). The Ecstasy Anti-
Proliferation Act of 2000 (Ecstacy Act), contained in Pub. L.
106-310, directed the Sentencing Commission to increase
penalties for ecstasy. Pub. L. 106-310 §§ 3663(a), 3664.
Accordingly, the Sentencing Commission promulgated a tem-
porary amendment to § 2D1.1 that increased this ratio to
500:1, effective retroactively as of May 1, 2001. The district
court relied on this temporary amendment in setting the base
offense level. Forrester argues that subjecting him to a height-
ened sentence pursuant to the temporary amendment violated
the ex post facto clause of the Constitution.

     1.    The end date listed in the indictment

   The indictment alleged that the conspiracy continued until
October 18, 2001. The indictment was reproduced in full in
the plea agreement. The plea’s “Factual Basis” section men-
tioned only a beginning date, stating that “[i]n or about
332               UNITED STATES v. FORRESTER
November, 2000, . . . Forrester entered into an agreement with
Alba, and others, to manufacture and distribute” ecstacy.

   [21] We have declined to treat “guilty pleas as admitting
factual allegations in the indictment not essential to the gov-
ernment’s proof of the offense.” United States v. Cazares, 121
F.3d 1241, 1247 (9th Cir. 1997). Forrester asserts that,
because “the date alleged in a section 846 indictment is not
an element of the offense,” the date in the indictment, even
though it was replicated in his signed guilty plea, was not part
of the admission. In Cazares, we held that the “appropriate
course is not, as the government argues, for the defendant to
delete this [end date] from the guilty plea, but rather, for the
government at the plea colloquy to seek an explicit admission
of any unlawful conduct which it seeks to attribute to the
defendant. Having failed to do so, the government must fol-
low the normal procedure of proving relevant conduct at sen-
tencing by a preponderance of the evidence.” Id. at 1248
(internal quotation marks omitted). There is no mention of an
end date in the plea agreement, nor did Forrester admit to one
at the plea colloquy. Therefore the temporary amendment,
which took effect after Forrester’s admitted start date of
November 2000, cannot apply to him under the current pos-
ture of the case. We therefore remand for resentencing.
Unless the government proves by a preponderance of the evi-
dence that the conspiracy continued until after the temporary
amendment became effective, Forrester should be sentenced
under the November 2000 50:1 ratio.

      2.   Effective Date of the 500:1 Ratio

   Forrester also argues that even if the October 18, 2001 end
date can be used for sentencing, the increased ratio of 500:1
did not become effective until November 1, 2001, at the earli-
est, because the temporary amendment was invalid. We agree
that the temporary amendment’s retroactivity was invalid, but
hold that the amendment became effective on June 6, 2001
when it was initially published.
                  UNITED STATES v. FORRESTER                333
   In United States v. DeLeon, the Eighth Circuit considered
whether the referenced temporary amendment violated the
Administrative Procedures Act (APA). 330 F.3d 1033, 1034
(8th Cir. 2003). The court analyzed the APA’s three-step rule-
making provisions, which require notice of the proposed rule,
a hearing or receipt and consideration of public comments,
and the publication of the new rule. Id. at 1036-38 (citing 5
U.S.C. § 553). The crux of the inquiry was the precise date on
which the amendment became effective. The DeLeon court
determined it became effective on June 6 (the publication
date) even though the publication listed a retroactive effective
date of May 1. 330 F.3d at 1036.

   [22] The court’s reasoning was two-fold. First, § 553(d) of
the APA ordinarily requires that a rule be published at least
30 days prior to its effective date and, upon a showing of
good cause, permits a rule to take effect immediately upon
publication. Id. Therefore, even if the good cause exception
applies, the earliest effective date would be the June 6 publi-
cation date. Second, the court considered whether the amend-
ments could be retroactive to May 1. Agencies cannot adopt
retroactive regulations “unless that power is conveyed by
Congress in express terms.” Bowen v. Georgetown Univ.
Hosp., 488 U.S. 204, 208 (1988). The government argued in
DeLeon that the emergency nature of the Ecstasy Act, read
together with the Sentencing Act of 1987, empowered the
Commission to make the amendment retroactive. DeLeon,
330 F.3d at 1036-37. The court disagreed, holding that the
“true effect of the 1987 Act is merely to imbue the Commis-
sion with the power to enact temporary rules that take effect
immediately without prior Congressional approval.” Id.
(emphasis added). The court reversed and remanded for
resentencing of DeLeon under the former, pre-Ecstasy Act
scheme. Id. at 1038. For the same reasons, we hold that the
amendment to § 2D1.1 became effective on June 6, 2001 (the
initial publication date). We also reject Forrester’s argument
that the effective date should be the November 1 final publi-
cation date rather than the June 6 initial publication date.
334                 UNITED STATES v. FORRESTER
Therefore, if on remand the district court finds by a prepon-
derance of the evidence that the conspiracy continued until at
least October 2001, then the enhanced 500:1 ratio was appro-
priately applied to Forrester’s sentence because it ended after
June 6 2001, when the enhanced ratio became effective.

  B.       Estimating Ecstasy Quantities

   [23] Under the Sentencing Guidelines, “[w]here there is no
drug seizure or the amount seized does not reflect the scale of
the offense,” a district court may estimate the quantity of the
drug and may consider “the size or capability of any labora-
tory involved.” U.S.S.G. § 2D1.1 cmt. n.12; see also United
States v. Putney, 906 F.2d 477, 479 (9th Cir. 1990). The gov-
ernment recommended a base offense level of 38 premised on
(1) a “theoretical maximum yield” (TMY) of 183.6 kilograms
(kilos) of ecstasy, as calculated by DEA chemist Skinner, (2)
an “actual yield” of 63.1 kilos of ecstasy, also calculated by
Skinner, and (3) a detailed “business plan” discovered at the
ecstasy laboratory suggesting that the conspiracy intended to
produce 440 kilos of ecstasy. Forrester argues that the con-
spiracy involved less than 60 kilos of ecstasy and that the
appropriate base level (using the 50:1 ratio) was 32. The dis-
trict court applied the 500:1 ratio and, without making spe-
cific findings as to the precise quantity of ecstasy involved,
concluded that the base offense level was 38.

      1.    Insufficient Findings as to the Amount of Ecstasy
            Involved

   Forrester claims that the district court failed to make spe-
cific findings regarding the parties’ factual disputes about the
amount of ecstasy involved, in violation of Federal Rule of
Criminal Procedure 32. In United States v. Carter, we held
that “[f]or each disputed fact upon which the district court
intends to rely in imposing the sentence, the district court
must make an explicit factual finding that resolves the dispute
                      UNITED STATES v. FORRESTER                         335
[or] must clearly state that the disputed fact was not taken into
account . . . .” 219 F.3d 863, 867 (9th Cir. 2000).

   Here, the district court held a lengthy hearing in which the
government presented evidence about the estimated yield,
which led to an extensive exchange between the parties
regarding the chemist’s theoretical yield estimate, the PSR,
the reliability of Alba’s statement corroborating that estimate,
and Alba’s business plan indicating that the goal of the con-
spiracy was to manufacture 440 kilos of ecstasy per month.
The district court must rule on each of these disputed facts
individually. See id. at 866-67. In doing so, the court ensures
meaningful appellate review and avoids “the unfairness that
would result to a defendant if prison or parole officials were
to rely on false allegations or uncorrected reports.” Id. at 866.

   [24] The district judge calculated a base level offense of 38
based on the “testimony of the chemist at trial, the grafts that
were seized from the lab up there, and just tangentially the
fact that the Ninth Circuit actually upheld the same base
offense level in Mr. Alba’s case.”9 Although the sentencing
hearing was very thorough, a specific finding was not made
as to the amount of ecstasy involved in the conspiracy.10
While a base offense level of 38 may well have been reason-
able, that particular level applies to a range of quantities
beginning at 60 kilos, so it cannot be used as a proxy for an
exact finding as to the amount of ecstasy involved in this case.

  [25] Since this case is being remanded for additional find-
ings as to the end date of the conspiracy, we also direct that
  9
    The finding that “the Ninth Circuit actually upheld the same base
offense level” for Alba was erroneous. That issue was not raised on appeal
in Forrester I. This error demonstrates the importance of having each find-
ing explained so that its merits can be assessed later.
   10
      The lack of a specific finding as to the amount of ecstasy has, in turn,
hampered us in determining whether the appropriate drug estimation
method was used.
336                 UNITED STATES v. FORRESTER
the district court make explicit findings on all contested issues
raised at sentencing, the most important of which is the
amount of ecstasy involved in the conspiracy.

      2.   The Amount of Ecstasy Involved

   Although the district court did not make explicit findings as
to the amount of ecstasy involved, it necessarily relied on
some implicit finding of quantity in determining the base
offense level. There are three criteria for approximations of
drug quantity. United States v. Kilby, 443 F.3d 1135, 1141
(9th Cir. 2006).

      First, the government is required to prove the
      approximate quantity by a preponderance of the evi-
      dence . . . which means that the district court must
      conclude that the defendant is more likely than not
      actually responsible for a quantity greater than or
      equal to the quantity for which the defendant is
      being held responsible. Second, the information
      which supports an approximation must possess suffi-
      cient indicia of reliability to support its probable
      accuracy. Third, since the sentence depends in large
      part upon the amount of drugs . . . and approxima-
      tion is by definition imprecise, the district court must
      err on the side of caution in approximating the drug
      quantity.

Id. (internal quotation marks omitted).

   We have repeatedly held that a court must “err on the side
of caution” when estimating drug quantity, Chase, 499 F.3d
at 1069, and when there are two “equally good measures” for
making a calculation under the guidelines, a court must select
the one “bringing the less punishment,” United States v.
Hardy, 289 F.3d 608, 614 (9th Cir. 2002). We have also dis-
couraged the use of a TMY analysis, and in individual cases
have deemed it an inappropriate methodology to calculate
                      UNITED STATES v. FORRESTER                         337
drug quantity. Chase, 499 F.3d at 1069 (“the relevant inquiry
[is] not what a theoretical maximum yield would be”).11 In
theory, the TMY would be permissible in the absence of more
conservative, equally reliable estimates. Where a lower
approximation is an “equally good measure,” however, a rule
calling for a conservative estimate is likely to be incongruous
with a method that calculates maximum yield.12

    Here, the government’s expert, DEA chemist Skinner, testi-
fied that one of his calculations was a maximum theoretical
yield of 183.6 kilos of ecstasy. In Chase, the government’s
expert had “quite candidly admitted that his calculation was
a maximum theoretical yield,” an approach that this court
found “unreliable as a method of estimating how much
methamphetamine [the defendant] produced.” Id. However,
Skinner also testified that “there is a wide range in the yield
. . . from lab to lab,” and that he had also calculated a substan-
tially lower “actual yield” of 63.1 kilos of ecstasy based upon
the quantities of seized materials. The actual yield assumed
that Forrester’s lab could achieve a “conservative” 50% yield
at each reaction state from the seized precursor chemicals,
instead of the 100% yield assumed in the TMY calculation.
The chemist based his estimates to some extent on his conver-
sation with Forrester’s co-conspirator Alba. The district judge
indicated that he had calculated the base offense level of 38
relying on, among other things, the testimony of the govern-
  11
      Forrester observes that the TMY result is particularly suspect in this
case because, “according to the government, the conspiracy was only able
to manufacture 24.6 kilos during the preceding year, but it would then sud-
denly produce 159 kilos with the seized chemicals.”
   12
      Theoretical yield calculations are clearly permissible; it is the use of
a maximum theoretical estimate that is problematic. See, e.g., United
States v. Williams, 989 F.2d 1061, 1073 n.5 (using the lower estimate of
a theoretical range); United States v. August, 86 F.3d 151, 153 (9th Cir.
1996) (same); United States v. Basinger, 60 F.3d 1400, 1410 n.5 (9th Cir.
1995) (explicitly “minimiz[ing] the potential for overestimating drug
quantity by adopting the expert’s most conservative figure”).
338               UNITED STATES v. FORRESTER
ment’s chemist, but did not specify on which of the two esti-
mates he was relying.

   [26] Since the district court did not make any explicit find-
ings about the amount of ecstasy involved when it imposed a
base offense level of 38, we need not reach the question of
whether the court relied on an improper method of calculating
the amount of ecstasy. However, we note that when there are
two reasonable methods of calculation, the district court
should select the measure that brings the lesser punishment,
Hardy, 289 F.3d at 614. Therefore unless, on remand, the dis-
trict court’s findings show that the TMY was the most reliable
method available to calculate the amount of ecstasy, the 183.6
estimate is likely too high.

   Forrester also claims that his sentence was substantively
unreasonable under 18 U.S.C. § 3553(a), but we decline to
reach this issue because we are remanding for additional find-
ings and resentencing.

                       CONCLUSION

   [27] For the foregoing reasons, we AFFIRM Forrester’s
conviction, VACATE his sentence, and REMAND for addi-
tional findings and resentencing in conformity with this opin-
ion.
