Diana Gonzales Buchanan, John Buchanan, Vernon Bonner, and Fedell Anderson appeal their convictions for various crimes arising out of their involvement in a crack cocaine conspiracy. We affirm the convictions of all the co-defendants. We affirm the sentences of Diana Gonzales Buchanan, Vernon Bonner, and Fedell Anderson. We vacate John Buchanan’s sentence on counts three and four, and remand for resentencing on whichever charge the government chooses to proceed with. We affirm John Buchanan’s sentence in all other respects.
I
Diana and John Buchanan distributed crack cocaine out of their home in Houston. An informant, Ernest “Easy” MeDay, began working with the Austin Police Department (“APD”) to build a ease against the Buchan-ans. MeDay had served as a middleman on some of the Buchanans’ Austin drug sales, and was facing drug charges of his own when *824 he agreed to help APD. John Buchanan contacted McDay to broker a drug transaction with another party in Austin. Pursuant to this transaction, John Buchanan, Fedell Anderson, Lawrence Crane, 1 and Vernon Bonner drove to Austin in Anderson’s 1985 Cadillac. The group drove to McDay’s apartment, and Bonner and Crane conducted an armed sweep of the premises to make sure that no one else was present. John Buchanan and Anderson then entered, and McDay proceeded to set up the sale.
After making the sale, the group went to a night club. John Buchanan, Anderson, and McDay went inside, where McDay phoned his APD contact and reported what had transpired. McDay also informed his APD contact that the group was armed, possibly with automatic weapons, and that the car contained a large amount of crack cocaine. APD officers proceeded to the night club and began surveillance on Anderson’s car. The officers testified that Crane never strayed more than a few feet from the car, standing next to or sitting inside the car at all times. Bonner apparently never exited the vehicle, but remained seated in the backseat of the car. The officers believed that the two men were guarding the car.
About forty-five minutes after the surveillance began, John Buchanan and Anderson exited the club, got back in the car, and proceeded up the street. Not far from the night club, a marked police car stopped the Cadillac. The police removed the men from the car and frisked each one, finding a loaded .380 caliber pistol in Crane’s belt. In securing the ear, the police also found a loaded, fully automatic 9 mm. weapon and a loaded, semi-automatic 9 mm. pistol with an extra magazine. The police arrested the four men and took the vehicle to the station, where the officers obtained a warrant to search the vehicle. The police found two baggies containing approximately 280 grams of crack cocaine “cookies” inside the left-rear fender well, under a plastic vent where the door closes.
About a week later, the Houston Police Department (“HPD”) went to the Buchanans’ home to execute an arrest warrant for Diana Buchanan on a state charge of “Combative Aggravated Assault.” 2 The officers were not oblivious to the Buchanans’ drug activities. The officers present were all members of a joint HPD and Bureau of Alcohol, Tobacco, and Firearms (“ATF”) anti-gang task force, which had been investigating the Bu-chanans for several months. An informant had indicated that the Buchanans were supplying Houston gangs with large quantities of crack cocaine, and officers had attempted to negotiate an agreement to purchase six ounces of crack cocaine from the Buchanans. In addition, APD had contacted HPD conсerning John Buchanan’s arrest in Austin, and had indicated to HPD that drugs might be found at the Buchanan home.
Upon arriving at the Buchanan residence, the police knocked, identified themselves, and announced to Diana Buchanan that they were there to arrest her. While still outside the house, the officers heard commotion from within and, fearing the destruction of evidence, forcibly entered the residence. The officers secured Diana Buchanan, and immediately conducted a “protective sweep” 3 of the premises. During this sweep, the officers discovered, in plain view, two loaded assault-style rifles. Further, upon entering the kitchen, one of the officers observed several large baggies containing white powder residue on the kitchen counter. The officer also observed white powder and small “rock” chunks on the kitchen counter, floor, and in the sink. The officers believed these substances to be cocaine. A “field test” confirmed that the substance in the baggies was cocaine. After securing the residence, the officers obtained a search warrant. In the ensuing search, officers discovered paraphernalia used to manufacture crack cocaine and *825 approximately 200 grams of crack and powder cocaine jammed into the toilet. The officers also seized a 1988 Jaguar and a 1985 Mercedes-Benz.
The district court charged the four defendants as follows: John Buchanan, Bonner, and Anderson with possession with intent to distribute cocaine base, in violation of 21 U.S.C. § 841(a)(1) and 18 U.S.C. § 2 (count one); John Buchanan, Bonner, Anderson, and Diana Buchanan with conspiracy to possess with intent to distribute cocaine base, in violation of 21 U.S.C. §§ 841(a)(1), 846 (count two), and with aiding and abetting each other in using or carrying a firearm during a drug-trafficking offense, in violation of 18 U.S.C. § 924(c) and 18 U.S.C. § 2 (count three); and John Buchanan with using and carrying a machine gun during a drug-trafficking offense, in violation of 18 U.S.C. § 924(c) (count four), possessing a machine gun, in violation of 18 U.S.C. § 922(o) (count five), and being a convicted felon in possession of a firearm, in violation of 18 U.S.C. § 922(g) (count six). All four defendants were tried before a jury. The jury convicted John Buchanan on all six counts. Anderson and Bonner were found guilty on counts one, two, and three. Diana Buchanan was found guilty on count two.
II
A
Diana Buchanan contends that the district court erred in denying her motion to suppress evidence seized from her residence following her arrest. She argues that field testing the white powder residue contained in several clear plastic baggies, found on the kitchen counter of her home, constituted an impermissible “search” in violation of her Fourth Amendment rights. Diana Buchanan maintains that all subsequently seized evidence of drug trafficking should have been excluded as the fruits of this unconstitutional search.
In reviewing a district court’s denial of a motion to suppress evidence, wе review factual findings for clear error and conclusions of law
de novo. United States v. Cardenas,
The exclusionary rule mandates that, “evidence obtained in violation of the Fourth Amendment cannot be used in a criminal proceeding against the victim of [an] illegal search and seizure.”
United States v. Calandra,
The “plain view” doctrine will justify a warrantless seizure if: (1) the officers lawfully entered the area where the items were located; (2) the items were in plain view; (3) the incriminating nature of the items was “immediately apparent”; and (4) the officers had a lawful right of access to the items.
Horton v. California,
The incriminating nature of an item is “immediately apparent” if the officers have “probable cause” to believe that the item is either evidence of a crime or contraband.
Hicks,
The officers who executed the arrest warrant for Diana Buchanan were experienced members of an HPD-ATF anti-gang task force. They were aware of purported drug activity at the Buchanan residence, and had been investigating the Buchanans for several months. The officers were also aware that Diana Buchanan’s husband had just been arrested in Austin on drug and gun charges. When the police officers knocked on the door and announced their presence, they heard commotion within the house. Upon entry, the officers conducted a protective sweep during which they observed two assault-style rifles, white powder and small rock crumbs on the kitchen counter, floor, and sink, and several clear plastic bags containing a white powder residue.
4
Based upon the totality of these circumstances, we hold that the officers had probable cause to believe that the white powder residue contained in the plastic baggies was contraband or evidence of a crime.
5
Accordingly, the officers could have lawfully seized the items.
See Brown,
Since the plain view doctrine would have supported a warrantless seizure of the evidence, a warrantless search of the items was also permissible.
6
Hicks,
B
Diana Buchanan next argues that the district court erred when it admitted into evidence two taped conversations between her and an HPD officer. Diana Buchanan maintains that the recording was never properly authenticated. A district court has broad discretion in determining whether or not a sound recording should be admitted.
United States v. Biggins,
The government has the burden of demonstrating that the recording, as played, “is an accurate reproduction of relevant sounds previously audited by a witness.”
Biggins,
The recording in question includes two conversations in which an undercover officer discusses purchasing cocaine with Diana Buchanan. At the conclusion of each conversation, another voice indicates the date and time of the conversations. Testimony established that both officers present during the recording (an undercover officer who attempted to negotiate the drug purchase and the officer who indicated the time and date of the conversations) could hear the conversations as they occurred. The officer who gave the time and date of the conversations testified that he had reviewed the tape being offered and could confirm that the tape was indeed the one that he and the undercover officer had made, and that the recording accurately represented thе conversations as they occurred. Further, this officer testified that after speaking with Diana Buchanan during her arrest, he was “convinced” that the voice on the tape was Diana Buchanan’s. Although the district court did not elicit testimony as to all the
Biggins
elements, the officer sponsoring the recording gave adequate testimony to support the recording’s reliability. All the voices were identified, and there was no intimation that the tape had been altered. Further, the testifying officer explained how the recording was made, and testified as to its accuracy. Accordingly, we cannot say that the district court abused its discretion in admitting the tape as an accurate reproduction of relevant conversations.
See United States v. Lance,
C
Diana Buchanan next argues that the district court erred in increasing her offense level for “possession of a firearm” where the jury acquitted her on the charge of aiding and abetting in using or carrying a firearm during a drug-trafficking offense (count three).
See
U.S.S.G., § 2Dl.l(b)(l) (“If a dangerous weapon (including a firearm) was possessed, increase by 2 levels.”).
*828
The district court’s decision to apply § 2Dl.l(b)(l) “is essentially a factual determination reviewable under the clearly erroneous standard.”
United States v. Rodriguez,
The fact that the jury found Diana Buchanan not guilty of using or carrying a firearm during a drug-trafficking offense, does not bar the district court from increasing Diana Buchanan’s offense level under § 2Dl.l(b)(l). While a conviction requires proof beyond a reasonable doubt, a district court may sentence a defendant within the Sentencing Guidelines on any relevant evidence that “has sufficient indicia оf reliability to support its probable accuracy.” U.S.S.G. § 6A1.3;
United States v. Edwards,
Ill
A
John Buchanan argues that the district court improperly enhanced his sentence for being the “organizer or leader” of
*829
the drug-trafficking organization.
See
U.S.S.G. § 3B1.1 (“If the defendant was an organizer or leader of a criminal activity that involved five or more participants or was otherwise extensive, increase by 4 levels.”). John Buchanan argues that no organization existed, and that if one did exist, it did not include five or more participants. Normally, we review a district court’s finding concerning a defendant’s role in the offense for clear error.
United States v. Bethley,
The district court found that the drug distribution organization in this case consisted of John Buchanan, Diana Buchanan, Bonner, Anderson, and McDay. The pre-sentence report also included several other regular purchasers from the Buchanans, and “other confidential informants in Houston, Texas.” Judging from the record, we cannot say that these findings amounted to plain error. There was ample evidence to support the district court’s finding that a drug-trafficking organization of five or more persons existed. Further, there was ample evidence that John Buchanan was the leader of this group. Testimony indicated that Crane and Anderson worked as “bodyguards” for John Buchanan, and that John Buchanan directed their actions. McDay’s testimony confirmed that on the night of the arrest in Austin, John Buchanan gave the others instructions, and they followed those instructions. Testimony also indicated that John Buchanan had control over the sale of drugs by his wife, Diana Buchanan. We hold that the district court did not commit plain error in finding John Buchanan to be the organizer or leader of this drug-trafficking group.
See
U.S.S.G. § 3B1.1 comment, (n.4) (“Factors the court should consider include the exercise of decision making authority ... and the degree of control and authority exercised over others.”);
see also United States v. Fierro,
B
John Buchanan next argues that his conviction on counts three and four, both for using or carrying a firearm during a drug-trafficking offense, violated the Double Jeopardy Clause. Count three charged John Buchanan with violating 18 U.S.C. § 924(c)
*830
for aiding and abetting in using or carrying two semi-automatic pistols during the crime of possession with intent to distribute cocaine base in violation of 21 U.S.C. § 841(a)(1). Count four charged John Buchanan with violating 18 U.S.C. § 924(c) for using or carrying a machine gun during the same predicate crime (possession with intent to distribute cocaine base) relied on in count three. As we have previously held, use of more than one gun during a single drug-trafficking offense will not support multiple counts under 18 U.S.C. § 924(c).
United States v. Privette,
IV
A
Bonner argues that the district court erred in overruling his Fed.R.Evid. 404(b) objection and admitting evidence of his prior cocaine delivery conviction. The district court admitted the evidence as relevant to Bonner’s “motive,” “state of mind,” or “intent” because Bonner’s defense was that
*831
he was an innocent bystander. We review the district court’s admission of prior convictions over objection under a heightened abuse of discretion standard.
United States v. Wisenbaker,
Evidence is relevant “if it makes the existence of any fact at issue more or less probable than it would be without the evidence.”
United States v. Williams,
After finding Bonner’s prior conviction relevant, the district court weighed the conviction’s probative value against its possible prejudicial effects. The probative value of extrinsic offense evidence “must be determined with regard to the extent to which the defendant’s unlawful intent is established by other evidence, stipulаtion, or inference.”
Beechum,
B
Bonner next argues that the district court erred in admitting the opinion testimony of two APD officers.
16
We review the district court’s evidentiary rulings for abuse of discretion.
United States v. Speer,
The record reflects that both testifying officers were experienced in investigating narcotics trafficking and drug-related crimes.
18
Because of their experiences, the officers were familiar with certain conduct and methods of operation unique to the drug distribution business, including the methods used by drug dealers to protect their illegal investments. The first officer testified thаt, in his opinion, Bonner’s and Crane’s actions indicated that they were guarding the car. This type of testimony is permissible because it is based on specialized knowledge, and is admitted to aid the jury in understanding a fact in issue — whether Bonner’s presence with the drugs was innocent or not. The second officer testified that, based on his experience, a person transporting $30,000 worth of crack cocaine and multiple firearms would not allow a complete outsider to ride in the car. This testimony was also permissible opinion testimony, based on the officer’s spe
*833
cialized knowledge.
19
It aids the jury in understanding the significance of Bonner’s presence in a car laden with narcotics and weapons.
20
Fed.R.Evid. 702;
Washington,
V
Anderson argues that the district court misapplied the Sentencing Guidelines in calculating his base offense level. Anderson maintains that the district court erred in attributing to him the drugs seized from the Buchanan residence in Houston.
22
A district court's findings about the quantity of drugs upon which a sentence should be based are factual findings, which we review for clear error.
United States v. Palomo,
In this case, there was evidence that Anderson had been involved with the Buchanans since 1987. Testimony indicated that Anderson always accompanied John Buchanan on his trips to deliver drugs in Austin, serving as John Buchanan’s bodyguard and “right-hand man.” Officers testified that they had observed Anderson’s maroon Cadillac parked in the Buchanans’ driveway in Houston, and it was Anderson’s car, driven by Anderson from Houston, that was used to transport the 280 grams of crack cocaine recovered in Austin. Judging from the record, we cannot say the district court erred in attributing the drugs seized from the Buchanan residence in Houston to Anderson. 23 Anderson’s involvement in this conspiracy seems to have been co-extensive with thе Buchanans. Having often transported drugs from the Buchanan residence to Austin, it was not only foreseeable that the Buchanans would have a significant amount of drugs in their Houston home, but the presence of those drugs fits squarely within the pattern of drug distribution evinced by the actions of the conspirators in this case. See U.S.S.G. § IB 1.3, comment. (n.2(ii)) (“In determining the scope of the criminal activity that the particular defendant agreed to jointly undertake ... the court may consider any explicit agreement or implicit agreement fairly inferred from the conduct of the defendant and others.”). Accordingly, we affirm the district court’s decision to attribute the cocaine seized in Houston to Anderson in calculating his base offense level, and uphold his sentence. 24
VI
For the foregoing reasons, we AFFIRM the convictions of all co-defendants. We AFFIRM the sentences of Diana Buchanan, Vernon Bonner, and Fedell Anderson. We VACATE John Buchanan’s sentence on counts three and four and REMAND for resentencing on whichever count the United States chooses to proceed with. We AFFIRM John Buchanan’s sentence in all other respects.
Notes
. Lawrence Crane, a juvenile, was not a party to this proceeding.
. This arrest warrant was unrelated to John Buchanan's arrest in Austin. The warrant arose instead from allegations that Diana Buchanan had shot another woman at a taco stand.
.See Maryland v. Buie,
. According to the record, the officer who first entered the kitchen during the protective sweep stated that it was "obvious" that cocaine residue and small chunks of rock cocaine were "all over the kitchen.”
. We emphasize that the fact that the officers chose to field test the substance does not indicate that they lacked probable cause to believe the residue was contraband. Testing for certainty’s sake will not, by itself, undermine an otherwise valid probable cause determination.
Cf. United States
v.
Prandy-Binett,
.This opinion should not be read to hold that the mere presence of white powder residue in a plastic bag, by itself, will always give rise to probable cause. We hold only that under the circumstances of the present case, the incriminating nature of the evidence found in plain view was "immediately apparent.” This factor distinguishes this case from the situation in
Hicks.
In
Hicks,
the officer’s search of the stereo was improper because, based upon his knоwledge and experience, he lacked probable cause to suspect that the equipment was stolen or evidence of a crime.
See Hicks,
. John Buchanan also asserts that the district court erred in admitting the evidence discovered subsequent to the field test at the Buchanan residence. Having held that the evidence was lawfully admitted, we need not address this argument.
. We distinguish this case from
United States v. Pofahl,
. Diana Buchanan also argues that the district court abused its discretion in sentencing her to the maximum possible sentence under the guidelines "in light of the unusual and tragic circumstances of Mrs. Buchanan’s background,” or, in the alternative, that the district court should have departed from the guidelines in sentencing her. There is no evidence that the district court failed to take into account Diana Buchanan’s "tragic circumstances.” The presentence report develops these factors, and the district court recognized that Diana Buchanan had travelled a "rocky road.” Nevertheless, the district court felt that the maximum sentence was the appropriate punishment. Judging from the record, we cannot say the district court abused its discretion by giving the maximum sentence. So long as the district court acts within the guidelines, a harsh sentence, in and of itself, does not constitute error.
See United States v. Ponce,
. John Buchanan argues that the punishment disparity between crack and powder cocaine constitutes racial discrimination in violation of his Fifth Amendment right to equal protection, and constitutes cruel and unusual punishment in violation of the Eighth Amendment. John Buchanan also argues that the guideline applicable to crack cocaine is unconstitutionally vague. We have consistently rejected these arguments and do so again.
See supra
note 9;
see also United States v. Cherry,
. In its brief the government concedes that sentencing John Buchanan on both counts three and four violated double jeopardy principles.
. John Buchanan also argues that his sentences under counts five and six were duplicitous of the firearm charges contained in counts three and four. This argument lacks merit. Counts three and four, applying 18 U.S.C. § 924(c), required only that the defendant use or carry a firearm during a drug-trafficking offense. Count five, alleging violation of 18 U.S.C. § 922(o), required the possession of an automatic weapon; and count six, applying 18 U.S.C. § 922(g)(1), required that the defendant not only possess a firearm, but that he also be a convicted felon. Thus counts five and six involve distinct elements not required by counts three and four. Under the test set forth in
Blockburger v. United States,
.Bonner argues that we should evaluate the relevance of the prior conviction as to each distinct count of the indictment. We decline to do so. Bonner offered the same defense to all counts of the indictment: that he was an innocent bystander. The prior conviction is relevant to show that Bonner did not innocently accompany his co-defendants, and this extends to all counts for which Bonner was charged as a member of the conspiracy (possession of crack cocaine with intent to distribute, conspiracy to possess with intent to distribute, and aiding and abetting in using or carrying a firearm during a drug-trafficking offense).
. Without the admission of the prior drug conviction, the government's evidence as to Bonner’s state of mind would have been limited to McDay's testimony concerning Bonner's use of a gun in sweeping his apartment, the officers’ observations at the night club, Bonner's presence in the car, and Bonner’s thumbprint on one of the gun magazines.
. We have previously held that in conspiracy cases "the mere entry of a not guilty plea sufficiently raises the issue of intent to justify the admissibility of extrinsic offense evidence.”
United States v. Prati,
. When asked about the significance of observing Bonner and Crane in the car outside the nightclub, one officer testified that "[i]t appeared that those two people were protecting something in that car.” The second officer stated his opinion that it would be unreasonable for persons trafficking crack cocaine worth $30,000 to have an uninvolved "outsider" in the car. Bonner timely objected to these answers as improper opinion testimony, but in both instances the district court overruled the objections.
. Bonner contends that the government did not qualify or proffer the police officers as expert witnesses, and that their testimony must, therefore, be reviewed as opinion testimony of lay witnesses. We disagree. "If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training or education, may testify thereto in the form of an opinion or otherwise.” Fed.R.Evid. 702 (emphasis added). The record reflects that the prosecution qualified the officers as experts during direct examination by questioning them and eliciting responses as to their experience and qualifications.
.The first officer, a 15-year veteran of the APD, was assigned to the repeat offender program and testified as to his "experience and training” in investigating drug-trafficking crimes. The second officer, a 12-year veteran, had served as a narcotics investigator for six and one-half years prior to his testimony.
. We also reject Bonner's argument that this testimony was impermissible "profile evidence.” In this case, the government did not seek to prove guilt by showing how a defendant fit a list of characteristics making up the “profile” of a drug courier.
See United States v. Williams,
. Bonner also contends that the officers’ opinions amounted to testimony as to his guilt. Since the determination of guilt is solely within the province of the trier of fact, an expert witness cannot give an opinion as to a criminal defendant's mental state or condition. Fed.R.Evid. 704(b). However, opinion testimony is permitted in regard to other ultimate issues. Fed. R.Evid. 704(a). Rule 704(a) provides that "[testimony in the form of an opinion or inference otherwise admissible is not objectionable because it embraces an ultimate issue to be decided by the trier of fact."
Id.
We have previously recognized the difference between an impermissible opinion on an ultimate legal issue and "a mere explanation of the expert’s analysis of facts which would tend to support a jury finding on the ultimate issue.”
United States v. Speer,
. Bonner further argues that the сumulative effect of the district court's evidentiary errors amounted to reversible error. Finding no evi-dentiary errors, we reject this contention.
. In response to Anderson’s objection to having the Houston drugs included in his sentence, the probation officer stated that Anderson’s involvement in the conspiracy was extensive enough that the substances seized in Houston were attributable to him. The district court agreed, stating that:
There’s no question in my mind that the jury was correct in convicting Mr. Anderson of the conspiracy. The presentence investigation shows Mr. Anderson’s relation to the Buchan-ans going back to 1.987. There’s no question that any of the narcotics found in that room or house in Houston were part of the conspiracy that had been going on for a long period of time and Mr. Anderson was part of it.
. Anderson argues that further evidence of his lack of involvement with the drugs seized in Houston is the significant difference in chemical purity of those drugs as cоmpared to the crack seized in Austin (80-85% pure in Austin, 62-70% pure in Houston). The divergence in purity between different quantities of drugs, however, will not negate a finding that the drugs are attributable to a co-conspirator if the test set forth in the guidelines is met.
See Smith,
. We also reject Anderson’s contention that the district court erred in admitting his prior drug possession convictions as evidence of intent or state of mind.
See supra
Part IV(A). Anderson put his state of mind and intent into issue by pleading not guilty and claiming that he had not intended to possess the crack cocaine or participate in the conspiracy. The prior drug possession convictions, however, make it more likely that Anderson had knowledge of and intended to participate in the crimes committed by this group.
See United States v. Willis,
