Leonel Ruiz was convicted of conspiracy to possess cocaine with intent to distribute, and possession of cocaine with intent to distribute. He was sentenced to 235 months imprisonment on each count, to run concurrently. He argues on appeal that the district court abused its discretion in admitting the testimony of two witnesses under Fed.R.Evid. 404(b), and that the evidence was insufficient to support the conviction. 1 He also challenges his sentence, contending that the district court erroneously imposed a two-level increase for possession of a gun, and erred in attributing 29 kilograms of cocaine to him in determining relevant conduct.
I.
On November 3, 1994, sheriff deputies working with the DEA stopped a pickup truck south of Milwaukee and found 3 kilograms of cocaine in a Miller beer 12-pack box behind the passenger seat. They also found a bottle of Inositol — a common cutting agent for cocaine — under the seat. Leonel Ruiz was riding in the passenger seat at the time of the stop, and was arrested along with the driver.
In a statement to DEA agents, Ruiz declared that he had spent the prior night with a male friend in Niles or Chicago, but could not recall the friend’s name or address. He stated that he drove directly from his friend’s house to a ranch owned by Ramon Navarro. When asked why he was wearing a pager, he said “I don’t know. Sometimes for work.” He then admitted that he was unemployed when asked where he worked. Finally, he disclaimed any knowledge of the cocaine in the truck.
Unbeknownst to Ruiz, the police had maintained surveillance on him since he left his home that morning. Through ground and air surveillance, DEA agents observed Ruiz leave his residence in Waukegan with his girlfriend and drive alone in his car to Navarro’s ranch. He parked the car near a small outbuilding, and later moved it to another location on the property. Ruiz and Navarro later drove from the ranch in the pickup truck that was stopped near Milwaukee.
A narcotics detection canine was brought to Ruiz’ car which was still parked at the ranch, and the dog alerted to the left rear quarter panel of the car and an area in the backseat near the driver’s side door. In the backseat area, a DEA agent found that the panel near the armrest had been removed, the screws were loose, and factory-installed insulation was removed, apparently creating a “trap compartment” often used by narcotics traffickers to transport narcotics. A search of the ranch revealed more cocaine and drug paraphernalia. Ruiz’ residence in Waukegan was also searched, yielding a 9mm semi-automatic handgun with an obliterated serial number and a small quantity of cocaine.
At trial, a number of witnesses testified about Ruiz’ drug trafficking. The testimony revealed that Ruiz would often meet people at hotels in Waukegan to conduct cocaine transactions. He was almost always armed when at the hotels. Ruiz also transported 2 to 4 kilograms of cocaine from Waukegan to Milwaukee each week. The government also presented testimony of prior narcotics transactions pursuant to *880 Federal Rule of Evidence 404(b). Eduardo Salurso and Jesus Diaz testified that they purchased cocaine in kilo quantities from Ruiz on some occasions from 1989 to 1992.
II.
We note at the outset that a number of Ruiz’ challenges, including his attack on the sufficiency of the evidence, are based upon challenges to the credibility of the witnesses. Credibility determinations by the jury will be reversed on appeal only in exceptional circumstances, such as “where it was physically impossible for the witness to observe that which he claims occurred, or impossible under the laws of nature for the occurrence to have taken place at all.”
United States v. Hach,
Ruiz challenges the admission under Rule 404(b) of evidence of other acts involving drugs, asserting that they bear no temporal relationship to the acts underlying the indictment. Rule 404(b) generally prohibits other crime evidence, but provides in relevant part that “[e]vidence of other crimes, wrongs, or acts ... may ... be admissible ... as proof of motive, opportunity, intent, preparation, plan, knowledge, identity, or absence of mistake or accident....” The government presented the testimony of witnesses Eduardo Salurso and Jesus Diaz regarding drug activity that took place between 1989 and 1992 involving Ruiz. The testimony was offered to establish Ruiz’ intent regarding the 1994 conspiracy, which is a proper purpose under Rule 404(b). The second part of the test, however, requires that the other acts be similar enough and close enough in time to be relevant to the matter in issue. Ruiz asserts that the testimony should have been excluded as too remote in time, because the acts occurred two years before the charged conspiracy. The analysis of “how long is too long” is a flexible one, and the answer depends on the theory for which the evidence is offered.
United States v. Torres,
Contrary to Ruiz’ apparent assumption, two years is not an inherently unacceptable gap under Rule 404(b). In fact, this court has upheld the admission of testimony under Rule 404(b) that involved gaps in time dramatically longer than two years.
See, e.g., United States v. Kreiser,
III.
Finally, Ruiz raises two challenges to his sentence. First, he argues that the district court erred in assessing a two-level enhancement for possession of a firearm, because the use of a firearm is not unusual in drug cases and thus not an aggravating circumstance under U.S.S.G. § 5K2.0. Moreover, he claims that the witness who testified that he routinely carried a gun was not credible. The district court’s credibility determination is not clearly erroneous. See, e.g., 18 U.S.C. § 3742(e) (“the court of appeals shall give due regard to the opportunity of the district court to judge the credibility of the witnesses, and shall accept the findings of fact of the district court unless they are clearly erroneous”). Moreover, Ruiz received a two-level increase under U.S.S.G. § 2Dl.l(b)(l), which applies because he possessed the gun during the offense. Section 5K2.0 was not applied, and thus his argument that guns are too common in drug transactions to be considered an aggravating circumstance under § 5K2.0 is frivolous.
Ruiz also challenges the district court’s assessment of the drug quantity in sentencing. First, Ruiz challenges the six kilograms that the court calculated based upon the testimony of Salurso and Diaz. Ruiz contends that those kilograms should not have been counted in determining relevant conduct under U.S.S.G. § 1B1.3, because the conduct lacked temporal proximity (and, again, because their testimony was not credible). Under U.S.S.G. § lB1.3(a)(2), conduct is relevant for sentencing purposes if it is part of the same course of conduct or common scheme or plan as the offense of conviction. In determining whether conduct meets that standard, courts examine the “similarity, regularity and temporal proximity of the incidents in question” to the offense of conviction.
United States v. Cedano-Ro-jas,
The government maintains that the conduct is relevant under our decisions in
United States v. Nunez,
In the present case, the two-year gap in time is not fully explained by non-volitional circumstances. For part of 1992, Ruiz was apparently incarcerated, and therefore that time period would not in itself signify a cessation of the course of conduct. The remaining years of non-activity, however, are not similarly reconciled. There is no explanation for the lack of drug activity from 1992 to 1994 which would attribute that gap to something other than an end of that course of conduct. Moreover, the crime alleged in the case was one that involved frequent cocaine deals. Testimony at trial indicated that the 1994 conspiracy involved weekly cocaine deliveries to Milwaukee. Given that regularity, the two-year period of inactivity is even more problematic. Finally, although the offense alleged is similar in kind to the earlier transactions, the participants in the offense of conviction are different from those in the 1989 to 1992 transactions with the exception of Ruiz himself.
Compare Ceda-no-Rojas,
That conclusion does not, however, require a remand for resentencing. The court found Ruiz was responsible for 29 kilograms of cocaine, placing him in the 15 to 50 kilogram range of the Guidelines. Even disregarding the 6 kilograms wrongly included, Ruiz still falls within that range. His challenge to the remaining *883 kilograms is based entirely on attacking the credibility of the witnesses against him. As we have earlier noted, however, his credibility attacks are without merit. Therefore, the court properly placed Ruiz in the 15 to 50 kilogram range. The conviction and sentence are AffiRmed.
Notes
. Ruiz also raised a claim of ineffective assistance of counsel, but he has withdrawn that challenge in order to preserve his right to develop it'in a possible § 2255 motion.
. The government relied entirely on
United States v. Cedano-Rojas,
