MEMORANDUM ***

Frederic Emanuel Scott appeals his conviction for unlawfully using or carrying a firearm in relation to a drug trafficking crime, in violation of 18 U.S.C. § 924(c). For the following reasons, we AFFIRM the district court’s judgment:

1. We find no violation of Fed.R.Evid. 704. An expert witness generally may offer an opinion on an ultimate issue to be decided by the jury, provided he does not opine directly on the ultimate issue of the defendant’s mental state. See United States v. Freeman, 498 F.3d 893, 906 (9th Cir. 2007); Fed.R.Evid. 704(b). Special Agent James Huskey offered no opinion on Scott’s mental state when Scott traded the weapon for cocaine. Instead, Huskey’s testimony demonstrated how the weapon could be readily “converted to expel a projectile by the action of an explosive,” thereby meeting the definition of a “firearm.” See 18 U.S.C. § 921(a)(3). Furthermore, because at least one other witness also testified that he was easily able to convert the weapon to an operable state, Huskey’s testimony was harmless even if erroneously admitted. See United States v. Wang, 49 F.3d 502, 504 (9th Cir. 1995). To the extent Scott argues that Huskey’s reading of the statute was improper, Scott did not object to this portion of Huskey’s testimony. We find no plain error as Scott’s substantial rights were not affected. Scott does not contend that the agent gave an incorrect definition, and we note that the district court correctly instructed the jury.

2. We also find no merit to Scott’s argument that the Government violated Fed.R.Evid. 404(b) by calling witnesses to testify about his prior cocaine transactions. The testimony concerned the witnesses’ cocaine transactions with Scott and/or Steve Berg, some of which occurred when both men were present.

*621The testimony tended to show a close association between Scott and Berg, as well as their heavy involvement in the drug trade. Although one of the witnesses, Julian Mathis, did not link Scott with Berg, his testimony further showed Scott’s involvement in cocaine dealing. As Scott denied an expectation of receiving cocaine from Berg in return for the firearm, the evidence tended to refute Scott and permit the jury to infer his true intent. See United States v. Howell, 281 F.3d 615, 628 (9th Cir. 2000). Furthermore, the district court gave a proper limiting instruction to the jury, which is a factor weighing in favor of admission of the evidence. See United States v. Montgomery, 150 F.3d 983, 1001 (9th Cir. 1998). We see no abuse of discretion by the district court.

AFFIRMED.