Today’s case presents an unusual issue: whether or not we should continue to adhere to Circuit precedent permitting conviction of certain felonies without proof of mens rea. Concluding that such a rule is aberrational in our jurisprudence — a jurisprudence largely based on the Anglo-Saxon common law — we discard it.
Facts
Defendant Joe Alvin Anderson was arrested for possessing two automatic pistols and various silencer parts in violation of a provision of the National Firearms Act, 26 U.S.C. § 5861.1 The weapons, along with several semi-automatic pistols, were found in a vault in Anderson’s home. The premises had been searched pursuant to a warrant covering both it and an adjacent business property also owned by Anderson; a magistrate had issued the warrant based upon the affidavit of a witness who had observed evidence of drug-dealing activity, primarily at the business address but also at Anderson’s residence. No prohibited substances were found during the search.
Anderson was tried and convicted on the weapons charges. He then appealed to our court, contending that there was no probable cause to support the warrant to search his house; that the jury instruction requiring for conviction only that he knew the guns were firearms in a general sense, as opposed to knowing that they were automatic weapons, was erroneous; and that the evidence was insufficient to support conviction on either count. A panel of our court affirmed. United States v. Anderson, 853 F.2d 313 (5th Cir.1988).
Writing for the panel majority, however, Judge Garwood strongly suggested that United States v. Vasquez, 476 F.2d 730 (5th Cir.), cert. denied, 414 U.S. 836, 94 S.Ct. 181, 38 L.Ed.2d 72 (1973), holding that proof of specific knowledge that a weapon is automatic is not required for a conviction, was wrongly decided, even though he was bound by that decision. Anderson, 853 F.2d at 317-21. Judge Jolly urged that Vasquez be reexamined en banc. Id. at 322 (Jolly, J., concurring). We granted rehearing en banc in order to reconsider our holding in Vasquez. 860 F.2d 166 (5th Cir.1988). We reverse the panel’s holding *1250on mens rea and overrule Vasquez, but adopt the panel’s treatment of the remaining issues.2
Background
The Act, 26 U.S.C. § 5861 et seq., prohibits the ownership or transfer of certain enumerated “firearms” that have not been registered and approved as required. As used in the Act, the word “firearms” is a term of art that includes primarily weapons thought to be of a military nature and of no legitimate use for sport or self-defense. Conventional revolvers and semi-automatic pistols are not among the covered “firearms” enumerated in section 5845; “machine guns,” however, are.3 The fully automatic pistols possessed by the instant defendant qualify as “machine guns,” as they will fire more than one round of ammunition in response to a single pull of the trigger. Section 5845(b).4
“Firearms,” such as machine guns, that fall under the Act are subject to elaborate registration and approval procedures. Sections 5812, 5841. In this case, Anderson was charged with violating section 5861(d), which makes it unlawful for any person to “... possess a firearm which is not registered to him in the National Firearms Registration and Transfer Record....”
A little over sixteen years ago, in United States v. Vasquez, 476 F.2d 730 (5th Cir.1973), a panel of our court construed a portion of the National Firearms Act to have been meant by the Congress to subject citizens innocent of any mens rea to the heavy fines and penalties provided by it — up to ten years imprisonment, up to a $10,000 fine, or both. Today, we reverse the judgment of the trial court and overrule that decision.
The Act and the Issue
The National Firearms Act is drafted in a peculiar manner. Reading through the first of its general provisions, Section 5841, one would at first think it a comprehensive enactment indeed. The first sentence of that section commences, “The Secretary shall maintain a central registry of all firearms in the United States.... ” Upon arriving at Section 5845, however, our reader, if he or she persevered so far, would discover that the term “firearms,” as used in the Act, is an extreme instance of usage in the manner that lawyers term “words of art.” Indeed, at no point in the Act is “firearms” used in its general dictionary sense, “A weapon from which a shot is discharged by gunpowder — usually used only of small arms.” Webster’s Third New International Dictionary Unabridged.
Instead, the term is defined in the Act so as to narrow its meaning vastly in most respects and vastly to expand it in a few, producing a statutory meaning of “firearm” that overlaps the area covered by the common meaning of the term to an insignificant degree only. Generally speaking, all such categories of ordinary rifles, pistols and shotguns as might be found in a gunshop are excluded from its meaning, with only a few easily-concealable items such as sawed-off shotguns included, along with machine guns. In addition, various items entirely outside the commonly understood sense of the term are included in the *1251Act’s definition of “firearms”: artillery pieces, mines, bombs, grenades and the like, along with silencers. In short, the term as used in the Act bears little if any correspondence to that in common usage, much as though the word “animal” were defined in some supposititious National Zoo Act to exclude all mammals, reptiles and birds except lions and tigers, but to include freight trains, teddy bears, feather-boas and halltrees. So much for the Act and its “firearms”: what signifies for present purposes is that knowing or proving that a thing is a firearm in the ordinary sense of the term tells almost nothing about whether it is a “firearm” for purposes of the Act; and of this, more later.
The issue on which we disagree with the earlier Vasquez holding is legally narrow but factually broad — that regarding semiautomatic weapons that have, without the changing of their external appearance, been altered by design or by the effects of use and wear so that they fire more than one shot at a pull of the trigger and so have become “machine guns” for purposes of the Act.
Countless numbers of semi-automatic weapons stand in the closets and gun cabinets of this land. Several of the most popular shotgun models, many handguns, and not a few rifles are autoloaders; and either wear and tear or a simple operation can convert any of these from a firearm in the ordinary sense into a “firearm” in the sense defined by the Act. Where, as here, the criminal charge is that of possessing such an arm — one that looks like only a firearm but is in fact a “firearm” — we conclude that a conviction should require that the charged party knew it was a “firearm” in the Act sense, not that he (or she) merely knew it was a firearm.5
Freed
In reconsidering the Vasquez decision, we turn first to United States v. Freed, 401 U.S. 601, 91 S.Ct. 1112, 28 L.Ed.2d 356 (1971), upon which it is largely based. We do so because if, as Vasquez maintains, this is apposite Supreme Court precedent, then we are bound by it and our inquiry is at an end. The Vasquez interpretation of Freed reads as follows:
In the majority opinion in Freed, Justice Douglas stated the following rule:
By the lower court decisions at the time [the Act was amended] the only knowledge required to be proved was knowledge that the instrument possessed was a firearm. See Sipes v. United States, 8 Cir., 321 F.2d 174, 179, and cases cited.
These two explicit references to Sipes and its cited cases, including [United States v.] Decker, [292 F.2d 89 (6th Cir.1961)], make it abundantly clear that Justices Douglas and Brennan used the term “firearm” in its general meaning, not in its technical statutory meaning.
476 F.2d 730, 731-32 (5th Cir.) cert. denied, 414 U.S. 836, 94 S.Ct. 181, 38 L.Ed.2d 72 (1973).
Our reading of Freed is otherwise.
What the Vasquez panel overlooked is that the issue upon which it was pronouncing was not before the Freed court at all and that the expressions from that opinion on which it founded its position are not even dicta upon the question that we face today, but merely observations along the way to decision of a different issue entirely. That issue, as shown both by the somewhat cryptic opinion of the Freed Court and by the briefs of the parties in that appeal, summarized at 28 L.Ed.2d 1007 et seq., was not the issue in today’s case— *1252which is whether the defendants could be convicted only if they knew what they possessed was a “firearm” in the Act sense or whether their knowledge merely that it was a firearm in the ordinary sense would suffice. Indeed, that neither was nor could have been the issue in Freed, for what the Freed defendants possessed was hand grenades; and hand grenades are not firearms in the general or dictionary sense at all. Such an issue was not before the Court, and the Court did not decide it. Indeed, it could not have done so, for — as is made embarrassingly clear by passages from the Government’s Freed brief, quoted in the margin — the Government conceded that it had to prove that the item possessed was known to the defendant to be a “firearm” in the Act sense.6
What it did decide is plainly shown by the full passage from the Court’s opinion, given in elided form above in the quotation from Vasquez:
The Act requires no specific intent or knowledge that the hand grenades were unregistered. It makes it unlawful for any person “to receive or possess a firearm which is not registered to him.” By the lower court decisions at the time that requirement was written into the Act the only knowledge required to be proved was knowledge that the instrument possessed was a firearm. See Sipes v. United States, 321 F.2d 174, 179, and cases cited.
401 U.S., at 607, 91 S.Ct., at 1117 (emphasis added, footnote omitted).7 And so it is that *1253all of the Freed language upon which Vasquez relied to decide the issue in today’s case was spoken by the Court in deciding an entirely different one: whether the Act requires “specific intent or knowledge that the hand grenades were unregistered.” And even as to this issue, the Freed Court observes that vicious intent was doubtless assumed by Congress to be present in such a case as that before it; speaking of the Act, it remarks that “[t]his is a regulatory measure ... which may well be premised on the theory that one would hardly be surprised to learn that possession of hand grenades is not an innocent act.” 401 U.S. at 609, 91 S.Ct. at 1118 (emphasis added).
One may well doubt, however, that the Court would have written “one would hardly be surprised to learn that possession of a .22 caliber target pistol is not an innocent act,” yet this is the effect of translating the Court’s hand grenade holding into a general one. Especially is this so in view of the sentence in the Court’s opinion immediately following that quoted:
They [the hand grenades] are highly dangerous offensive weapons, no less dangerous than the narcotics involved in United States v. Balint, 258 U.S. 250, 254, 66 L.Ed. 604, 606, 42 S.Ct. 301, where a defendant was convicted of sale of narcotics against his claim that he did not know the drugs were covered by a federal act.
Ibid.
Finally, in his separate concurrence (quoted elsewhere by the Vasquez panel), Justice Brennan cautions “that mens rea is not a unitary concept, but may vary as to each element of a crime; ...” 401 U.S. at 613, 91 S.Ct. at 1120. He also observes— and the Freed majority does not dispute— that “[t]he Government and the Court agree that the prosecutor must prove ... knowledge that the items possessed were hand grenades.” Id. at 612, 91 S.Ct. at 1119.
In sum, it is readily apparent that Freed did not decide the issue that is before our Court and that, therefore, it in no way trammels our judgment in today’s case. And what it does offer goes against the view of Vasquez.8
The Automatic Semi-Automatic
As we have noted, under the Vasquez construction of the Act it is possible for one to be guilty of a felony punishable by severe penalties by innocently possessing— perhaps by inheritance, for example — a semi-automatic pistol, say, which has become a machine gun by alteration or by wear and tear. That such consequences should attend mere ignorance or failure to investigate an apparently legal item is aberrational in our legal system.
Although Section 5861(d) does not contain express wording — such as “knowingly” — imposing a mens rea requirement, it is well settled that “far more than the simple omission of the appropriate phrase from the statutory definition [of the offense] is necessary to justify dispensing with” a mens rea requirement. Liparota v. United States, 471 U.S. 419, 426, 105 S.Ct. 2084, 2088, 85 L.Ed.2d 434 (1985), quoting from United States v. United States Gypsum Co., 438 U.S. 422, 438, 98 S.Ct. 2864, 2874, 57 L.Ed.2d 854 (1978). Several Supreme Court cases have so stated, and this seems to be beyond reasonable controversy. See Liparota, supra; United States v. Bailey, 444 U.S. 394, 406 n. 6, 100 S.Ct. 624, 633 n. 6, 62 L.Ed.2d 575 (1980); United States v. United States Gypsum Co., supra. See also Morissette *1254v. United States, 342 U.S. 246, 250, 72 S.Ct. 240, 243, 96 L.Ed. 288 (1952); LaFave & Scott, Substantive Criminal Law § 5.1 at 579 (1986) (“the absence of words in the statute requiring a certain mental state does not warrant the assumption that the legislature intended to impose strict liability; to the contrary, at least for an offense as serious as bigamy, it should be presumed that the legislature intended to follow the usual mens rea requirement ‘unless excluded expressly or by necessary implication.’ ”) (footnote omitted.)
It is one thing for the Court to liken hand grenades to narcotics, as it did in Freed; quite another to draw such a parallel where ordinary skeet guns or target rifles are concerned. For the National Firearms Act does not treat conventionally manufactured, normal revolvers, semi-automatic pistols, hunting rifles, or shotguns as anything other than perfectly innocent, legal items. It does not purport to create any presumptions about any such items, or to regulate them in any manner. Common sense tells us that millions of Americans possess these items with perfect innocence. It is unthinkable to us that Congress intended to subject such law-abiding, well-intentioned citizens to a possible ten-year term of imprisonment if — unknown to them, and without reasonable cause on their part to think otherwise — what they genuinely and reasonably believed was a conventional semi-automatic pistol turns out to have worn down into or been secretly modified to be a fully automatic weapon.9 In both Liparota, supra, and United States Gypsum, supra, — each of which were pure statutory offense cases — the Court reapproved Justice Jackson’s famous language in Morissette, 342 U.S. at 250, 72 S.Ct. at 243, that:
The contention that an injury can amount to a crime only when inflicted by intention is no provincial or transient notion. It is as universal and persistent in mature systems of law as belief in freedom of the human will and a consequent ability and duty of the normal individual to choose between good and evil.
And in Lambert v. California, 355 U.S. 225, 229, 78 S.Ct. 240, 243, 2 L.Ed.2d 228 (1957), the Court, in striking down on due process grounds a strict liability offense, noted:
As Holmes wrote in The Common Law, ‘A law which punished conduct which would not be blameworthy in the average member of the community would be too severe for that community to bear.’
We think it far too severe for our community to bear — and plainly not intended by Congress — to subject to ten years’ imprisonment one who possesses what appears to be, and what he innocently and reasonably believes to be, a wholly ordinary and legal pistol merely because it has been, unknown to him, modified to be fully automatic.10 Certainly we have not done this for other offenses. Even for the misdemeanor offense of shooting over a baited field, United States v. Delahoussaye, 573 F.2d 910 (5th Cir.1978), we imposed a “should have known” standard respecting strict liability. And, in United States v. Panter, 688 F.2d 268 (5th Cir.1982), we created a self-defense exception to the offense of possession of a pistol by a felon, noting that criminal statutes should be interpreted “ ‘against a background of Anglo-Saxon common law’ ” — which certainly *1255requires mens rea for felonies — and that “[t]he government’s theory of absolute liability ascribes to § 1202(a)(1) an effect ‘more comprehensive than was contemplated and one inconsistent with our philosophy of criminal law.’ Morissette v. United States, 342 U.S. at 250, 72 S.Ct. at 243.” Panter, 688 F.2d at 271; see also United States v. Boerner, 508 F.2d 1064, 1067-68 (5th Cir.1975) (implying knowledge requirement in 8 U.S.C. § 1324(a)(1) offense). Vasquez’s interpretation of the National Firearms Act is likewise “inconsistent with our philosophy of criminal law” and not within the intent of Congress.
Stare Decisis
For the reasons stated above, we are satisfied that our Vasquez panel (a truly eminent one, but Horace advises us that Homer himself hath been observed to nod) misread Freed and laid down a rule unintended by Congress and incongruent with our Anglo-Saxon legal traditions. Our en banc court now addresses the issue for the first time.
In such circumstances, where a wrong turn has been taken, back is the shortest way forward. Only last spring, the Supreme Court overturned one of its own thirty-six year old statutory constructions because convinced it was a mistaken one. Rodriguez de Quijas v. Shearson/Ameri-can Express, Inc., — U.S. -, 109 S.Ct. 1917, 104 L.Ed.2d 526 (1989).11 Nor has our en banc court hesitated to do so, e.g. Bhandari v. First National Bank of Commerce, 829 F.2d 1343 (5th Cir.1987), vacated, — U.S. -, 109 S.Ct. 3207, 106 L.Ed.2d 558 (1989), (overruling fifteen year old construction of 42 U.S.C. § 1981); International Woodworkers of America v. Champion International Corporation, 790 F.2d 1174, 1175-76, 1180-81 & n. 8 (5th Cir.1986), aff'd sub nom. Crawford Fitting Co. v. J.T. Gibbons, Inc., 482 U.S. 437, 107 S.Ct. 2494, 96 L.Ed.2d 385 (1987) (overruling, in an opinion joined by ten of the presently active judges of this Court, at least four prior Fifth Circuit decisions construing 28 U.S.C. §§ 1821 & 1920 and 42 U.S.C. § 1988); Sparks v. Duval County Ranch Co., Inc., 604 F.2d 976, 983 (5th Cir.1979), aff'd sub nom. Dennis v. Sparks, 449 U.S. 24, 101 S.Ct. 183, 66 L.Ed.2d 185 (1980) (overruling several prior Fifth Circuit decisions on 42 U.S.C. § 1983 immunity).12
We overrule Vasquez, under which innocent possession of a worn or altered auto-loader can result in jail time. Such a rule is unjust and dangerous, and there is little if any need for it. For in most cases, as in this one, mens rea will be proveable if it exists.13
*1256 Conclusion
Except as to the jury instruction on knowledge, we adopt the rulings of the panel opinion. As to it, we reverse Anderson’s conviction and remand for further proceedings consistent with today’s decision. It is so
ORDERED.
. The two pistols are identical in appearance to semi-automatic models that can be lawfully purchased and owned without registration under the Act. These guns had been made automatic by modification of their internal mechanisms; it is disputed whether a non-expert could discern this without firing them. Accompanying the pistols was a manual on how to modify semi-automatic pistols into fully automatic ones. The silencer parts found were insufficient to form a fully-assembled silencer. However, one portion found was, even in its incomplete state, capable of muffling a gunshot to some extent.
. In his en banc brief, in addition to contesting the rule established by Vasquez, defendant raises the same fourth amendment defective-warrant and sufficiency-of-the-evidence challenges disposed of by the panel. He also argues for the first time that the district court’s definition of "silencer” in its jury instructions, given in accordance with a statute enacted subsequent to his arrest, violates the constitutional prohibition of ex post facto laws. We do not consider novel contentions at this stage of proceedings, however.
. For those unfamiliar with firearms terminology, it may be helpful to offer a few definitions. An "automatic” weapon or "machine gun” is one which commences firing when the trigger is depressed and continues firing until it is released, or the weapon’s supply of ammunition is exhausted. A "semi-automatic" weapon or "auto-loader" is one which fires only one shot when the trigger is depressed but which reloads itself, so that when the trigger is released and again depressed it fires again, and so on. To add to the confusion, shooters usually refer to semi-automatic weapons as “automatics,” doubtless because they reload themselves automatically by employing some of the explosive force of the round last fired.
.Unless otherwise noted, section references hereinafter are to title 26 U.S.C.
. In fact, making this latter sort of semi-scienter an element of proof of the offense produces very strange consequences indeed. In the first place, any person likely to be charged under the Act will surely know that the object which he or she possesses is a firearm in the general sense, so that such proof is no proof at all. In the second, as we have noted, many firearms in the general sense are not "firearms" in the Act sense at all, so that knowledge that one possesses a firearm in the general sense tells little or nothing about knowing that you have one in the Act sense. And finally, what of items such as silencers and land mines, which are not firearms in the general sense at all? Are the elements of proof to be deemed different where they are concerned?
. At pages 7 and 8 of the “Brief for the United States” in Freed, filed by then Solicitor General Griswold on December 3, 1970, appears a passage which the Court partly incorporated in its opinion, quoted in text on the next page:
The district court erred in construing Section 5861(d) as requiring as an element of the government's proof a showing that the transferee obtained possession of a firearm with specific knowledge and intent that the firearm be unregistered. The statute contains no language suggesting the need for such proof, and the history of its predecessors, both in Congress and in the courts, conclusively shows that such a construction has never been thought to be part of the statute, or necessary to save the statute from constitutional doubt. All that the government needs to show is that the individual charged possessed the firearm which was unregistered, with knowledge that it was a firearm, and with intent to possess it.
Given the extremely dangerous character of firearms subject to the Act, it is inaccurate to characterize such a construction as imposing a penalty "for conduct alone without regard to the intent of the doer.” Lambert v. California, 355 U.S. 225, 228 [78 S.Ct. 240, 242, 2 L.Ed.2d 228 (1957) ]. The very nature of the weapons is sufficient to apprise an individual possessing them that they are likely to be regulated, and thus is also sufficient to make a failure to inquire as to the lawfulness of the possession culpable behavior in the ordinary sense. Hand grenades are certainly no less dangerous than narcotic drugs, as to which similar penalties have always been found proper. United States v. Balint, 258 U.S. 250, 254 [42 S.Ct. 301, 303, 66 L.Ed. 604 (1922) ].... The government must show that appellees were in possession of hand grenades, knowingly and intentionally; but it need not show any knowledge or intent on their part that these grenades be unregistered (emphasis added throughout).
The same brief also states (p. 25): "To be sure, there must be some evidence of mental state— that the accused knew he possessed a firearm and that he intended to be in possession;_” (Emphasis added.)
. As we have noted, Vasquez took the position that the word "firearm” in the above quotation referred to firearms in the common usage of that word, not "firearm" as defined in the Act. However, nothing in the Act supports that analysis, because the Act simply does not deal at all with firearms in the commonly understood meaning of the word.
Nor does Sipes support that construction. In Sipes, the defendant was apprehended running away from the police, carrying a rifle having a fourteen and a half inch barrel. It had a nail for a firing pin, and when test fired was found to fire on the first attempt. The defendant testified that when he initially found the weapon it did not have a firing pin. The Court observed that "the inference that [defendant] Sipes inserted the nail is proper and creates a knowing ‘making’ on his part.” 321 F.2d at 179. There was no contention that Sipes was unaware of any of the physical characteristics of the weapon. The Sipes court noted that in some other decisions it had been stated that “ ‘scienter is not involved’ ” in such offenses, citing United States v. Decker, 292 F.2d 89, 90 (6th Cir.), cert. denied, 368 U.S. 834, 82 S.Ct. 58, 7 L.Ed.2d 36 (1961), but went on to say, "[W]e need not go so far_ There can be no question that the defendant’s possession of the weapon was a knowing one.” 321 F.2d 174, 179 (8th Cir.), cert. denied, 375 U.S. 913, 84 S.Ct. 208, 11 L.Ed.2d 150 (1963).
And as for Decker, the Sixth Circuit has rejected it as of this writing. See United States v. Williams, 872 F.2d 773 (6th Cir.1989).
. Subsequent Supreme Court references to Freed indicate that it is considered as establishing a mens rea requirement concerning knowledge of the relevant physical characteristics of the items possessed. Thus, in United States v. International Minerals & Chemical Corp., 402 U.S. 558, 91 S.Ct. 1697, 1699, 29 L.Ed.2d 178 (1971), the Court observed: "Here as in United States v. Freed [citation], which dealt with the possession of hand grenades, strict or absolute liability is not imposed;_" If Freed sanctioned conviction for possession of a machine-gun where the defendant reasonably believed that what he possessed was a conventional semiautomatic pistol, then it would have imposed strict liability. In United States v. United States Gypsum Co., 438 U.S. 422, 436, 98 S.Ct. 2864, 2873, 57 L.Ed.2d 854 (1978), Justice Brennan’s concurring opinion in Freed is cited in support of a mens rea requirement.
. Nothing in the legislative history suggests otherwise. Rather, it is quite clear that Congress was at great pains to disclaim the imposition of any burden on those who possessed ordinary firearms for hunting, self-protection, or the like. See Pub. Law 90-618, section 101, 82 Stat. 1213; Pub. Law 99-308, section 1(b), 100 Stat. 449.
. We are puzzled in this regard by the dissenting opinion’s reiterated references to a duty of inquiry. On p. 1261, for example, the opinion states that “the pertinent question is whether Congress intended to place on the owner a reasonable duty of inquiry; by far the better view is that it did." Again on p. 1261, the dissent states that “a minimal burden of inquiry imposed upon the gun owner is a reasonable component of Congress’s policy." The significant thing about these observations is that they are inconsistent both with our Vasquez decision, with the instructions given in this case, and with the government's litigating position here, none of which recognizes any sort of “reasonable inquiry” doctrine and each of which would impose strict felony liability whether or not the defendant acted reasonably.
. In addition to the cases cited in Rodriguez, supra, see also, e.g., the following decisions overruling prior holdings on issues of statutory construction: Monell v. Department of Social Services, 436 U.S. 658, 98 S.Ct. 2018, 2038, 56 L.Ed.2d 611 (1978); Continental TV, Inc. v. GTE Sylvania, Inc., 433 U.S. 36, 97 S.Ct. 2549, 53 L.Ed.2d 568 (1977); Peyton v. Rowe, 391 U.S. 54, 88 S.Ct. 1549, 20 L.Ed.2d 426 (1968); Nye v. United States, 313 U.S. 33, 61 S.Ct. 810, 817, 85 L.Ed. 1172 (1941).
. Moreover, posl-Vasquez congressional silence is not of great significance, given the split in the circuits, the lack of authoritative Supreme Court guidance, and the fact that Freed, if anything, points away from Vasquez, Further, both citizen reliance and subsequent congressional inaction are of significantly diminished persuasiveness as bases for adhering to a prior decision where the challenge to that decision is that it expanded the scope of criminally proscribed conduct beyond that intended by the enacting congress. There are no federal common law crimes, and Congress may not retroactively expand the reach of criminal statutes.
.Our dissenting siblings disagree, pointing out how greatly the prosecution is assisted in convicting persons accused of this felony if not required to prove state of mind and suggesting that establishing such a mental state may sometimes be difficult (Ms. op. 294). The first observation is undoubtedly true, but may be felt by some to prove too much: conviction of any felony — from murder on down — is facilitated by removing the intent element of proof.
As for the second suggestion, one found in possession of an automatic semi-automatic, like one found in possession of powdered cocaine, may decline to testify and argue through counsel that he did not know what it was that he had. Given that a jury can ordinarily infer knowledge of their nature from the possession of such illegal items and the surrounding circumstances, however, this seems a dangerous course of action and one likely to lead to conviction. Perhaps this is why such a contention rarely succeeds in narcotics cases.