dissenting in part:
My colleagues reverse defendant Spinner’s assault weapon conviction because they conclude that the evidence was insufficient to sustain the charge, and reverse his narcotics conviction because they conclude that the district court permitted prejudicial eross-ex- • amination of Spinner’s girlfriend. I disagree with both conclusions and would affirm both convictions.
I. The Gun
The majority holds the government’s evidence insufficient' on the assault weapon charge because they believe it “failed to present any evidence on an essential element” of the crime: to wit, that the AR-15 assault rifle possessed a “pistol grip that-protrudes conspicuously beneath the action of the weapon.” The government presented no evidence on this point, my colleagues say, because the government’s expert failed to mention the word “action” during his testimony. But the expert’s failure is beside the point. The government did not need an expert’s testimony to establish this element because it had much better evidence: it had the gun itself.
A photograph of the gun is attached to this opinion. See App. 1 (Gov’t Ex. 48-C). Its “pistol grip” is quite prominent, and the majority does riot suggest that the jury would have any trouble figuring out which part of the gun was the “pistol grip.” Nor does the majority, or the defendant, contend that the word “conspicuously” was too vague for the jury to comprehend. Only the meaning of “action” is in dispute. But that dispute is simply irrelevant. The photograph clearly shows that the pistol grip protrudes conspicuously beneath every part of the weapon, whatever that part’s name. Hence, even if the jury had no idea what the word “action” meant, as long as it understood the “action” to be a part other than the “pistol grip” itself, it is hard to see how a rational trier of fact could reach any conclusion other than that this element of the crime was satisfied.
The majority’s citation to the Seventh Circuit’s opinion in United States v. Meadows, 91 F.3d 851 (7th Cir.1996), does not support its conclusion, but the way in which that ease differs from this one is instructive. First, there was no evidence in that case that the weapon at issue had a rifled, as compared to a smooth, bore — the key statutory feature. It was not just that the jury’s attention had not been drawn to the issue. Even by the time of the appeal, the record did not indicate what kind of bore the weapon had. The court found that the weapon “may have contained either a smooth bore or a rifled bore,” because “[t]he record nowhere indicates which.” Indeed, “[t]he old pistol ... may well not have had a rifled bore.” Id. at 857. That is not the case here. The attached photograph makes clear that the AR-15 did have the necessary element — a protruding pistol grip.
Second, the Meadows court found that even if the weapon actually had a rifled bore, there was no way for the jury to know that without “look[ing] down the barrel.” Id. Since the Meadows jury had no reason to *963know that looking down the barrel was important, the court found no reason to believe the jury would have “bothered” to do so. Id. But .no such “bother” was required of Spinner’s jury. The expert — whatever else his failings — held the gun up directly in front of the jury, and both the gun and the attached photograph (Appendix 1) were admitted into evidence. As long as the jurors had their eyes open during either the testimony or their own deliberations, they necessarily would have seen the essential element.
The majority also accepts Spinner’s argument that even if the government did prove the AR-15 was a prohibited weapon, it failed to prove he had the required mens rea. As Staples v. United States, 511 U.S. 600, 114 S.Ct. 1793, 128 L.Ed.2d 608 (1994), makes clear, and as the majority agrees, the government needed to prove only that Spinner knew the gun had the feature in question; it did not have to prove he knew the feature was, illegal. See Bryan v. United States, — U.S. —, -, 118 S.Ct. 1939, 1946, 141 L.Ed.2d 197 (1998). This means the government needed to prove only that Spinner knew the gun had a pistol grip protruding conspicuously beneath the action.
How could the government meet that requirement? Surely it did not have to present evidence that Spinner was told the weapon’s grip extended in that way. We do not expect defendants to have their own personal ATF experts on hand to advise them of their weapons’ special features.1 Under Staples,the defendant’s knowledge “can be inferred from circumstantial evidence, including any external indications signaling the nature of the weapon.” Id. at 615 n. 11, 114 S.Ct. 1793. We held in United States v. Moore, 97 F.3d 561, 564 (D.C.Cir.1996), for example, that a defendant’s knowledge that a sawed-off rifle was shorter than the lawful sixteen inches could be inferred from the fact that length is readily observable. No evidence that the defendant ever measured the weapon’s 13-1/16-inch barrel was required, even though the difference between that and a 16-ineh barrel is less than obvious to the naked eye. See also United States v. Foster, 19 F.3d 1452, 1454 (D.C.Cir.1994) (“The readily apparent barrel length and general appearance of the sawed-off rifle ... are sufficient . to establish that its owner knew the weapon needed to be regis-tered_”). By contrast, the “external indication” of the nature of the AR-15 is obvious to the naked eye and no guess about its specific length is required. Accordingly, the only question is whether Spinner ever saw or handled the gun.
The majority suggests there was no such evidence. To be sure, there was no such direct evidence: no one testified to seeing Spinner with the gun. But the law has no preference for direct evidence over circumstantial, see Moore, 97 F.3d at 564, and often it is the latter that is the more reliable. Courts regularly affirm murder and bombing convictions notwithstanding the absence of an eyewitness who saw the defendant shoot the gun or light the fuse. See, e.g., United States v. Kwong, 14 F.3d 189, 193-94 (2d Cir.1994). Indeed, in Moore we found sufficient proof that the defendant knew the sawed-off rifle was too short based on the fact that he had control of the weapon through constructive possession — even without evidence that he ever handled the weapon after it had been sawed off. Id. at 564. Here, too, the jurors could reasonably rely on a wealth of circumstantial evidence that Spinner saw or handled the weapon. See Staples, 511 U.S. at 615 n. 11, 114 S.Ct. 1793.
First, there was more than enough evidence for a reasonable juror to conclude that a well-armed drug operation was based in Spinner’s family home and employed the AR-15 in its work. The house was filled with all of the accoutrements of such an operation: semi-automatic weapons, magazines of extra ammunition, a bulletproof vest, two black ski masks, crack cocaine and zi-plock bags. Moreover, a narcotics expert testified, based on the evidence recovered in the search, that the house was being used as a “stash house” from which narcotics sales were made. In such a business, the expert said, guns are used for intimidation and the *964maintenance of control. Given this evidence, the jury was entitled to conclude it was no coincidence that the AR-15 was in the house, and that instead it was an integral part of the business’ armament.
Second, there was more than enough evidence that Spinner was a participant in the drug operation, and that as such he would have handled or seen others handle the weapon. When the police entered the house, he was the only adult male present. His fingerprints were on a bullet inside a cracks-tained gun, on the container of a magazine of spare bullets, and on a list of current crack prices. Two undercover officers testified that they purchased twenty-five ziplocks of crack from him at the same house nine months before. The majority does not dispute the introduction of that evidence which, our cases hold, is probative of the fact that Spinner intended to possess and distribute the drugs found during the search, and tended to disprove his claim of mere innocent presence in the house.2 The jurors were also told that the defendant previously had possessed unlawfully a semiautomatic weapon which, again, our cases hold “make[s] it less probable that the [weapons] found in the [house] ... were there by mistake or without [the defendant’s] intent.” United States v. Brown, 16 F.3d 423, 432 (D.C.Cir.1994); accord United States v. Toms, 136 F.3d 176, 183-84 & nn. 11-12 (D.C.Cir.1998). With this evidence, the jury could readily have concluded that as a player in the operation, Spinner would either have handled or seen others handle the AR-15. See Toms, 136 F.3d at 183 (evidence of participation in drug conspiracy sufficient for jury to conclude that defendant had dominion and control over weapon not found on his person).
Finally, there also was specific evidence that the assault rifle belonged to Spinner or was under his direct control. The gun was found in a half-opened case in an open closet in an upstairs bedroom. Whoever lived in that bedroom plainly had control over the contents of the closet. And there was plenty of evidence for a jury to conclude that the bedroom was Spinner’s. The police found a photo of him lying on the floor of the bedroom with his feet resting in the open closet. Inside the bedroom were several letters to Spinner postmarked in 1996, the last one dated just seven days before the search. Also in the bedroom were the kinds of personal identification a person needs for daily living, and that one would be unlikely to leave behind after moving out. These included Spinner’s Social Security card, his cheek-cashing card, two medical assistance passes in his name, and a club membership ■ card. (Spinner’s current car registration was found in the living room.) Spinner’s fingerprints were found in the bedroom — on a current list of crack prices. They were also found in the closet itself — on a container of ammunition placed right next to the half-opened case containing the AR-15.
Our cases have repeatedly upheld jury findings of a defendant’s actual or constructive possession of an item of contraband based on far more tenuous evidence than that offered by the government here.3 There is no reason to treat this case differently. Accordingly, I would conclude that the evidence was sufficient to show both that the AR-15 assault rifle had a conspicuously protruding pistol grip and that defendant knew it did.
*965II. The Drugs
My colleagues reverse the defendant’s narcotics conviction on the' ground that the district court abused its discretion by permitting cross-examination of Spinner’s girlfriend about a letter she wrote' him. The majority concludes the district court erred because the letter was not admissible as a prior “bad act” under Rule 404(b). The letter did not describe a prior bad act, the majority says, because it did not appear to refer to prior drug dealing at all. But even if the letter were admissible under Rule 404(b), the majority holds, the district court still erred in permitting cross-examination because the government failed to provide reasonable notice that it planned to do so.
There is no need to address the question of whether the district court abused its discretion,4 because the kind of error just described could not have been legally harmful to the defendant. To conclude that the error was harmful, and therefore grounds for reversal, we must conclude that it “affected substantial rights,” Fed.R.Crim.P. 52(a). This “means that the error must have been prejudicial; It must have affected the outcome of the district court proceedings.” United States v. Olano, 507 U.S. 725, 734, 113 S.Ct. 1770, 123 L.Ed.2d 508 (1993). I cannot reach that conclusion here.
If the majority is correct in its description of the letter, it can hardly have been harmful. According to the court, the letter created either no inference, or such a weak inference, of prior drug dealing that it could not be admitted under Rule 404(b).5 It is not “at all apparent,” the majority says, that the reference in the letter was “to crack cocaine.... Nor is it clear that the reference is to narcotics at all. Under these circumstances, the statements in the letter have virtually no bearing on whether Spinner possessed crack cocaine with the intent to distribute it in this case.” But under these circumstances, the letter also could not have had a prejudicial effect. If the references were only to “drinking and cursing and laying up,” as Ms. Little contended, it is hard to see what prejudicial impact they could have had in a ease filled *966with evidence of crack cocaine and assault weapons and bulletproof vests.
This conclusion is further bolstered by considering what actually transpired at the trial. The prosecutor asked Ms. Little whether certain phrases in her letter referred to drugs. The phrases themselves did not contain the word. Ms. Little said no, repeatedly and adamantly. No other evidence as to the meaning of the letter was offered. Although the prosecutor did argue very briefly that the references must have been to drugs, the judge gave the usual limiting instruction that lawyers’ arguments are not evidence and that the verdict must be based only on evidence. We have repeatedly said this kind of instruction can mitigate the impact of improper jury argument. See, e.g., United States v. Gatling, 96 F.3d 1511, 1524 (D.C.Cir.1996); United States v. Childress, 58 F.3d 693, 716 (D.C.Cir.1995). With this extraordinarily weak evidence, it is hard to see how the defendant could have been prejudiced.
On the other hand, if a reasonable jury could have read the letter as referring to prior drug dealing by Spinner, then permitting the cross-examination was not error in the first place. If the letter did refer to prior drug dealing, it would have been admissible under Rule 404(b) to show Spinner’s intent to possess and distribute the drugs found in the search — just as the district court held, see Trial Tr. 997-99 (Feb. 10, 1997), and just as the prosecutor argued to the jury, Trial Tr. 1151 (Feb. 11, 1997). The majority does not dispute this, and a host of our cases so hold. See supra note 2.
But, the majority contends, even if the cross-examination were permissible under Rule 404(b), the district court still abused its discretion because the government failed to give the defense “reasonable notice” of its intent to use the letter. Yet, a failure of notice alone cannot justify reversal. The defendant still must have suffered prejudice. See United States v. Perez-Tosta, 36 F.3d 1552, 1562 n. 9 (11th Cir.1994). Since this contention by the majority starts from the assumption that the evidence was admissible under Rule 404(b), the prejudice could not have come from the failure to give the defendant more time to argue that the evidence was inadmissible. Nor could the prejudice have come from defense counsel’s lack of time to prepare the witness. What better answer could Miss Little have given to the government’s pestering questions than the response she did give: “Not ... drugs.... I know nothing of drug things.” In any event, although the government did not file a Rule 404(b) notice, the letter was hardly the “complete surprise” defense counsel claimed it to be since the government had given it to counsel during discovery.
Finally, as against this extraordinarily weak evidence of prejudice — whether derived from the cross-examination itself or from the failure to give.notice — we also must weigh the evidence arrayed against the defendant. Although the government’s case may not have been “overwhelming,” it did not have to be to establish harmless error. It only had to be strong enough to persuade us that whatever mild prejudice may have flowed from the cross-examination, it did not “substantially sway[ ]” the ultimate verdict. United States v. Clarke, 24 F.3d 257, 267 (D.C.Cir.1994).
The majority finds the government’s evidence thin because “no fingerprint evidence connected Spinner to the crack.” But while Spinner’s fingerprints were not on the crack itself, they were on a list of current crack prices and on a bullet inside a crack-laced gun. And most of the crack itself was found inside the bedroom closet that appeared to be his. This, together with the other evidence recounted above, was strong evidence that Spinner was a member of the drug operation that used his mother’s home as a “stash house.” In any event, whatever inference of prior drug dealing the letter generated, it surely was weaker than, and “harmlessly cumulative” of, see Clarke, 24 F.3d at 267, the much more direct evidence of Spinner’s prior dealing properly admitted through the testimony of the two undercover officers who bought twenty-five ziplocks of crack from him.
And against all of this, what was the defendant’s theory of the case? It was that none of the contraband was his, 'and instead all belonged to his 17-year-old cousin, Darryl Henkle. Henkle did indeed testify that the guns, the drugs, the ammunition, and the other indicia of drug-dealing in the house were all his; that Spinner knew nothing of *967any of it; and that he had never, ever, seen Spinner with drugs. Henkle came to court to testify against his own interests, he told the jury, in order “[t]o clear my cousin’s name because he shouldn’t have to go to jail for something that I did.” Trial Tr. 868 (Feb. 10,1997).
This must have been quite a lot for any rational juror to swallow. The jury was advised that the 17-year-old previously had pled guilty in juvenile court to charges involving “possession of these firearms and the drug evidence in this case,” had received a sentence of “house arrest and community service,” id, and could not “be farther prosecuted,” id. at 949. Mr. Henkle, then, had nothing at risk and only his cousin to save by bravely taking all the weight upon himself. Moreover, Henkle was caught in a bold-faced lie while trying to do just that. He testified that he had found all of the guns in a car owned by Spinner’s brother Robert, after Robert was shot to death in 1995, and that he had hidden them in the house without Spinner’s knowledge. There was only one small problem: an official from the Sturm-Ruger Company testified that the Sturm-Ruger pistol found in the house had not even been shipped from the factory until two months after Robert was killed.
The cross-examination which the majority and I have addressed at length took no more than a few minutes out of a week-long trial. It was one of dozens of such evidentiary rulings in the course of that trial. In recognition of the real-life context in which such rulings are made, and the cost to the rule of law if every mistake required a retrial, we review such trial court decisions only for abuse of the court’s discretion. See, e.g., United States v. Graham, 83 F.3d 1466, 1473 (D.C.Cir.1996). Moreover, even where there is such an abuse, Federal Rule of Evidence 103(a) instructs us that “[ejrror may not be predicated upon a ruling which admits or exeludes evidence unless a substantial right of the party is affected,” and Federal Rule of Criminal Procedure 52(a) provides that “[a]ny error, defect, irregularity or variance which does not affect substantial rights shall be disregarded.” See United States v. Russo, 104 F.3d 431, 434 (D.C.Cir.1997). Because Spinner’s substantial rights were not affected by the cross-examination of his girlfriend, I would affirm his conviction for possession with intent to distribute crack cocaine.
Accordingly, I dissent from the majority’s reversal of the two convictions discussed above, while concurring in the majority’s af-firmance of the remaining convictions.
*968ATTACHMENT Appendix 1 (Gov’t Ex. 48-C)
. The juiy could well have concluded that the defendant was something of a weapons expert himself. He previously had been convicted of illegal possession of a TEC-9 semi-automatic pistol, and the police found an advertisement for a book about assault weapons in a bedroom the jury rationally could have believed was his. See infra.
. See, e.g., United States v. Robinson, 59 F.3d 1318, 1322 (D.C.Cir.1995); United States v. Johnson, 40 F.3d 436, 441 n. 3 (D.C.Cir.1994); United States v. Clarke, 24 F.3d 257, 265 (D.C.Cir.1994); United States v. Washington, 969 F.2d 1073, 1080-81 (D.C.Cir.1992).
. See, e.g., Toms, 136 F.3d at 183-84 (evidence of prior drug dealing and that drugs were found in car was sufficient to prove that driver had constructive possession of weapon on seat of other occupant); In re Sealed Case, 99 F.3d 1175, 1179-80 (D.C.Cir.1996) (evidence that drugs were found near items tied to defendant was sufficient to establish actual or constructive possession); United States v. Fennell, 53 F.3d 1296, 1299-1300 (D.C.Cir.1995) (evidence that defendants had keys and had just left apartment was sufficient to establish actual possession of contraband in apartment); United States v. Harrison, 931 F.2d 65, 72-73 (D.C.Cir.1991) (evidence that defendant intended to distribute drugs was sufficient to prove defendant had constructive possession of guns found on other occupants of car); see also United States v. Jackson, 124 F.3d 607, 610-11 (4th Cir.1997) (evidence that firearm was stored at defendant’s mother’s home was sufficient to show constructive possession).
. The majority states that the government undertook the cross-examination to rebut the defendant’s claim that he had become a "changed man” and no longer was involved in drug dealing. My colleagues say that permitting such a rebuttal was an abuse of discretion because it is barred by Rule 404(b) as an argument about the defendant’s character: i.e., a contention that Spinner was not a changed man. But if Spinner actually had presented such a defense, the government surely would have been permitted to rebut it. The Federal Rules of Evidence do not give defendants a free pass to present claims the government is barred from rebutting. If rebutting a "changed man” defense constitutes an effort to prove the defendant’s character (and I am not sure that it does), then presenting such a defense must constitute such an effort as well. That is, by claiming that he is a changed man, Spinner must be claiming that he could not have committed the crime charged because he had changed his character and become law-abiding. But if that is his claim, then Rule 404(b) is not the rule that governs this case: Rules 404(a) and 405(a) are. And those rules permit the prosecution to cross-examine'as to specific instances of past conduct in order to rebut a claim of good character advanced by the defendant. See United States v. Roper, 135 F.3d 430, 433 (6th Cir.1998); United States v. Moore, 27 F.3d 969, 974 (4th Cir.1994); 2 Jack B. Weinstein & Margaret A. Berger, Weinstein’s Federal Evidence § 404.11 [2] (2d ed.1998); 1 John W. Strong, McCormick on Evidence ! 191 (4th ed.1992).
I do not dissent on this ground, however, because in fact the defendant never offered any evidence in support of a changed man defense. Defense counsel’s opening statement did suggest that defense and indicated it would be proven through the testimony of defendant’s mother. But Spinner’s mother never testified and defense counsel did not return to the argument in his closing.
. The inference would have to have been quite weak to justify the majority's determination that it was inadmissible on this score. All the government needed to prove with respect to probativeness was that " 'the jury could reasonably find the conditional fact — [here, that the defendant had engaged in drug transactions in the past] — • by a preponderance of the evidence.' ” Clarke, 24 F.3d at 264 (quoting Huddleston v. United States, 485 U.S. 681, 690, 108 S.Ct. 1496, 99 L.Ed.2d 771 (1988)) (brackets in original). Thus, the majority’s determination of inadmissibility means the inference could not meet even that minimal threshold. Indeed, the majority’s determination means the inference must have been even weaker than that. In order to reverse the trial judge’s conclusion that the letter did show prior drug dealing, the majority had to find the inference so weak that the judge’s conclusion whs an abuse of discretion. See United States v. Graham, 83 F.3d 1466, 1473 (D.C.Cir.1996).