                             In the

    United States Court of Appeals
               For the Seventh Circuit
                   ____________________

No. 17-1335
DELFINO RODRIGUEZ-CONTRERAS,
                                                       Petitioner,
                               v.

JEFFERSON B. SESSIONS III, Attorney General of the United
States,
                                               Respondent.
                   ____________________

              Petition for Review of an Order of the
                 Board of Immigration Appeals.
                         No. A017 046 772.
                   ____________________

   ARGUED OCTOBER 4, 2017 — DECIDED OCTOBER 12, 2017
               ____________________

   Before BAUER, EASTERBROOK, and MANION, Circuit Judges.
    EASTERBROOK, Circuit Judge. An alien who has been con-
victed of an “aggravated felony” as defined in 8 U.S.C.
§1101(a)(43) is removable from the United States. Section
1101(a)(43)(E) specifies that any violation of 18 U.S.C.
§922(g)(1) counts as an aggravated felony. Section 922(g)(1)
in turn bars anyone who has been convicted of a felony from
possessing a firearm. The Board of Immigration Appeals
2                                                  No. 17-1335

concluded that these statutes require Delfino Rodriguez-
Contreras, a citizen of Mexico who had been admitted for
permanent residence, to leave the United States without any
possibility of discretionary relief from removal. See 8 U.S.C.
§§ 1227(a)(2)(A)(iii), 1229b(a)(3).
    After having been convicted of a felony in Illinois, Rodri-
guez-Contreras was found in possession of a weapon and
convicted of violating 720 ILCS 5/24–1.1(a). He spent 30
months in prison for that crime. If the elements of the state
offense match the elements of §922(g)(1), then Rodriguez-
Contreras must be removed. The question is not what he did
in fact but what elements must be established to secure a
conviction—in other words, whether the state statute “cate-
gorically fits within the ‘generic’ federal definition of a cor-
responding aggravated felony.” Esquivel-Quintana v. Sessions,
137 S. Ct. 1562, 1568 (2017), quoting from Moncrieffe v. Holder,
569 U.S. 184, 190 (2013).
   Rodriguez-Contreras contends that 720 ILCS 5/24–1.1(a)
does not match the federal crime because the state statute
bars felons from possessing pneumatic weapons as well as
those that use explosives. The Board did not address this ar-
gument. Instead it stated that Negrete-Rodriguez v. Mukasey,
518 F.3d 497 (7th Cir. 2008), and Estrada-Hernandez v. Lynch,
819 F.3d 324 (7th Cir. 2016), have held that a violation of 720
ILCS 5/24–1.1(a) is an aggravated felony, so there was no
work for the Board to do.
   The Board’s treatment of our decisions assumes that to
address one legal argument is to address all possible legal
arguments. Negrete-Rodriguez argued that the Illinois and
national felon-in-possession crimes do not match because
the state statute omits the interstate-commerce element that
No. 17-1335                                                      3

§922(g)(1) contains. We rejected that contention and held
that courts consider statutes’ substantive elements rather
than provisions that allocate prosecutorial authority. 518
F.3d at 501–03. See also Torres v. Lynch, 136 S. Ct. 1619 (2016)
(a state crime covered by §1101(a)(43) is an aggravated felo-
ny when it matches the federal crime in all but the commerce
element). Our decision in Negrete-Rodriguez did not say
whether the substantive elements of the state and federal
statutes match, because the alien had not presented an ar-
gument on the subject. Nor did the alien in Estrada-
Hernandez. How the substantive elements of 720 ILCS 5/24–
1.1(a) mesh with those of §922(g)(1) has never been resolved
by this court. Now is the time.
    Section 922(g)(1) prohibits the possession of a “firearm”
by someone who has been convicted of a felony. The word
“firearm” is defined in 18 U.S.C. §921(a)(3) as “any weapon
… designed to … expel a projectile by the action of an explo-
sive”. Any violent release of gas produces an “explosion” in
common usage; think of a volcano, which propels tons of
rock miles into the air when gas dissolved in magma comes
out of solution and creates powerful pressure. But §921(a)(3)
does not ask whether an explosion pushes the projectile out
of the weapon; it asks whether an explosive does the work.
Compressed air is not an explosive, which means that
pneumatic weapons are not “firearms” under federal law.
See, e.g., United States v. Castillo-Rivera, 853 F.3d 218, 225 (5th
Cir. 2017) (en banc); United States v. Crooker, 608 F.3d 94, 96
(1st Cir. 2010); Bureau of Alcohol, Tobacco, Firearms and
Explosives Ruling 2005–4.
   Illinois law, by contrast, defines a firearm as “any device,
by whatever name known, which is designed to expel a pro-
4                                                  No. 17-1335

jectile or projectiles by the action of an explosion, expansion
of gas or escape of gas” with exceptions, including one for
pneumatic guns that have a muzzle velocity less than 700
feet per second. 430 ILCS 65/1.1. The Attorney General’s
brief concedes that this definition makes the state law broad-
er than the federal law but contends that it is farfetched to
think that possessors of air rifles would be prosecuted in Il-
linois. In the Attorney General’s view the state and federal
statutes match as a practical matter despite the linguistic dif-
ference. Yet a recent decision by the Appellate Court of Illi-
nois shows that felons are indeed prosecuted for and con-
victed of possessing air rifles. People v. Thompson, 2017 IL
App (3d) 160503 (Sept. 6, 2017).
    Air-powered weapons can be as deadly as those that use
explosives to generate the gas that propels the bullet; a
pneumatic mechanism can give a bullet quite a kick. Sher-
lock Holmes called Sebastian Moran the second most dan-
gerous man in London (behind only Moriarty) because he
killed at a distance with an air rifle, a quiet weapon that al-
lowed him to avoid detection. See A. Conan Doyle, The Ad-
venture of the Empty House, in The Return of Sherlock Holmes
(1905). It does not surprise us that Illinois prosecutes felons
who possess such weapons. This means that the state statute
is indeed broader than its federal counterpart and, under the
reasoning of Esquivel-Quintana and its predecessors, cannot
be treated as an “aggravated felony.”
    The immigration judge supported her decision with a
fallback argument: that the Illinois statute is “divisible” and
permits immigration officials (and judges) to look at the
charging papers and other documents to see which statutory
provision was involved. The IJ treated 720 ILCS 5/24–1.1(a)
No. 17-1335                                                     5

as creating distinct offenses: possession of a (federally de-
fined) firearm by a felon, and possession of an air rifle by a
felon. The IJ also found that the weapon that led to Rodri-
guez-Contreras’s conviction used explosives; she concluded
that this marks the particular crime Rodriguez-Contreras
committed as an aggravated felony. (Rodriguez-Contreras
observes that Smith & Wesson, the manufacturer of his
weapon, made some .22 caliber air pistols, but he does not
contend that his .22 caliber pistol was air-powered.)
    The Attorney General’s brief in this court does not de-
fend the IJ’s divisibility ruling. Mathis v. United States, 136 S.
Ct. 2243 (2016), distinguishes between multiple crimes codi-
fied under a single heading (divisible) and multiple ways of
committing a single crime (not divisible). Illinois has estab-
lished only a single crime of weapon possession by a felon.
In Illinois there are multiple ways of committing that crime
(possessing a powerful air rifle is one, possessing a weapon
that uses explosives is another), but a definitional clause
does not create a separate crime.
    It follows that a violation of 720 ILCS 5/24–1.1(a) is not an
“aggravated felony” and that federal law does not foreclose
Rodriguez-Contreras’s ability to receive discretionary relief
from removal. In exercising discretion the Board and IJ are
free to consider the fact that Rodriguez-Contreras possessed
a weapon that comes within the scope of a federal prohibi-
tion as well as a state prohibition. Moncrieffe, 569 U.S. at 204.
All our decision establishes is that his state conviction does
not prevent immigration officials from exercising discretion
as they deem appropriate.
    Whether it will be necessary to exercise discretion is open
to question. When the removal proceeding began, the agen-
6                                                 No. 17-1335

cy’s sole stated reason for deeming Rodriguez-Contreras
removable was his conviction of an aggravated felony; the
administrative prosecutor did not rely on any of Rodriguez-
Contreras’s other convictions or contend that his felon-in-
possession conviction, shorn of the aggravated-felony char-
acterization, justifies removal. The first order of business on
remand therefore will be to determine whether this removal
proceeding should be dismissed outright.
   The petition for review is granted and the matter is re-
manded to the Board for proceedings consistent with this
opinion.
