PUBLISH 

UNITED STATES COURT OF APPEALS 

FOR THE TENTH CIRCUIT 

_________________________________ 

UNITED STATES OF AMERICA, 

 Plaintiff - Appellee, 

v. 

SCOTT RAY BISHOP, 

 Defendant - Appellant. 

No. 18-4088 

_________________________________ 

Appeal from the United States District Court 

for the District of Utah 

(D.C. No. 2:16-CR-00662-DB-1)

_________________________________ 

Jessica Stengel, Assistant Federal Public Defender (Scott Keith Wilson, Interim Federal 

Public Defender, with her on the briefs), Office of the Federal Public Defender for the 

District of Utah, Salt Lake City, Utah, appearing for Appellant. 

Ryan D. Tenney, Assistant United States Attorney (John W. Huber, United States 

Attorney, with him on the brief), Office of the United States Attorney for the District of 

Utah, Salt Lake City, Utah, appearing for Appellee. 

_________________________________ 

Before BRISCOE, HOLMES, and McHUGH, Circuit Judges. 

_________________________________ 

BRISCOE, Circuit Judge. 

_________________________________ 

This is a direct criminal appeal from Defendant Scott Bishop’s convictions on 

one count of unlawfully manufacturing machineguns, in violation of 26 U.S.C. 

§ 5861(a), and one count of unlawfully possessing or transferring machineguns, in 

FILED 

United States Court of Appeals 

Tenth Circuit 

June 10, 2019

Elisabeth A. Shumaker 

Clerk of Court
2 

violation of 18 U.S.C. § 922(o). A machinegun is “any weapon which shoots, is 

designed to shoot, or can be readily restored to shoot, automatically more than one 

shot, without manual reloading, by a single function of the trigger.” 26 U.S.C. 

§ 5845(b). “The term . . . also include[s] . . . any part designed and intended solely 

and exclusively, or combination of parts designed and intended, for use in converting 

a weapon into a machinegun . . . .” Id. Defendant designed and manufactured a 

device, referred to as a TCGTR, that he intended his customers to install in their 

AR-15 semiautomatic rifles to increase the speed at which their guns fired. The 

government offered evidence that the TCGTR was a machinegun because it increased 

an AR-15’s rate of fire by causing the gun to fire multiple bullets per pull of the 

trigger. 

Defendant, who proceeded pro se at trial, took the stand in his own defense 

and testified that he did not intend the TCGTR to convert an AR-15 into a 

machinegun. The district court excluded portions of Defendant’s testimony after 

finding that it was expert testimony not properly disclosed to the government. 

Defendant, now represented by counsel on appeal, argues that the jury’s verdict 

should be set aside because the district court denied him his constitutional right to 

present a defense, erred when instructing the jury on the elements of a § 5861(a) 

offense, improperly admitted hearsay testimony about the legality of the TCGTR, and 

allowed unsupported expert testimony on an ultimate issue of fact. Exercising 

jurisdiction pursuant to 28 U.S.C. § 1291, we affirm. 
3 

I 

In 2015, the Bureau of Alcohol, Tobacco, Firearms and Explosives recovered a 

“machine gun conversion device” while executing a search warrant in an unrelated 

case. App. Vol. III at 77. The device “had paperwork with it that explained how it 

worked and it had pictures on it that showed how [to] install th[e] device.” Id. The 

paperwork indicated that the device was sold by a company called “TCGTR” through 

a website called “arfakit.com.” Id. Using state business registration records, ATF 

linked the TCGTR business and arfakit.com to Defendant. 

A TCGTR1

 is a small piece of metal that, when properly bent according to 

Defendant’s instructions, fits inside an AR-15. 

[T]he “TCGTR” (trigger control group travel reducer) was a custommade metal device, approximately 2.4 inches in length, and 

approximately 1/2 inch at its major width. As sold by [Defendant], 

the . . . device required one[ ]final bend for the device to become 

operational as a machinegun. The purchaser could . . . go back to 

[Defendant’s] website . . . and obtain the instructions on how to 

complete the device. The device is premarked at the bend location 

with a stencil. . . . [Defendant also] gave his customers very detailed 

written instructions, including photos, for making the final bend to 

their [TCGTRs]. [Defendant] also sold a “raw materials” variation 

of his kit, which was the same kit, but a flat piece of metal that 

required a total of four bends. 

App. Vol. II at 18. As part of its investigation, ATF ordered multiple TCGTRs from 

Defendant and, after following Defendant’s instructions for bending and installing a 

TCGTR, tested the effect on an AR-15. 

 1

 The TCGTR is also referred to as a “kit” or “device.” 
4 

“The AR-15 is the civilian version of the military’s M-16 rifle, and is, unless 

modified, a semiautomatic weapon.” Staples v. United States, 511 U.S. 600, 603 (1994). 

A semiautomatic “weapon . . . fires only one shot with each pull of the trigger.” Id. at 

602 n.1. Conversely, an “automatic” or “fully automatic” “weapon . . . fires repeatedly 

with a single pull of the trigger. That is, once its trigger is depressed, the weapon will 

automatically continue to fire until its trigger is released or the ammunition is exhausted. 

Such weapons are ‘machineguns’ within the meaning of the [National Firearms] Act[, 26 

U.S.C. §§ 5801–5872].” Id. Based on its testing, ATF concluded that the TCGTR was a 

machinegun because it caused an AR-15 to “fire[] automatically more than one round 

without manually reloading it with a single function of the trigger.” App. Vol. III at 468. 

In December 2016, Defendant was indicted for violating 26 U.S.C. § 5861(a) by 

“knowingly engag[ing] in the business of manufacturing and dealing in firearms, to wit: 

machinegun conversion devices for AR-15 style rifles, without having paid the special 

occupational tax . . . and without having registered” with the federal government. App. 

Vol. I at 14. Defendant was also indicted for violating 18 U.S.C. § 922(o) by “knowingly 

possess[ing] and transferr[ing] machineguns, to wit: machinegun conversion devices for 

AR-15 style rifles.” Id. Defendant represented himself at the jury trial with the 

assistance of standby counsel. At the hearing held pursuant to Faretta v. California, 422 

U.S. 806 (1975), Defendant acknowledged that he would “be required to comply with all 

of the court rules and the Rules of Procedure and the Rules of Evidence and all of the 

rules and procedures that pertain in a jury trial.” App. Vol. III at 4. 
5 

At trial, the government called ATF Special Agent Michael Powell to testify as an 

expert about why the TCGTR was a machinegun. He explained that an AR-15 contains a 

part called a disconnector that “prevent[s] the firearm from firing a second shot without 

[the operator] releasing the trigger and then pulling it a second time.” Id. at 486. Powell 

then explained that the TCGTR “overrides or negates the function of the disconnector 

while the trigger is pulled and the weapon is” firing. Id. He testified that, by disabling 

the disconnector, the TCGTR allows an AR-15 to “fire[] automatically.” Id. at 468. In 

Agent Powell’s expert opinion, this meant that the TCGTR met “the statutory definition 

of a machinegun” in 26 U.S.C. § 5845(b). Id. at 469. 

When it was Defendant’s turn to present his case, he testified about his design for 

the TCGTR. Defendant acknowledged that he designed the TCGTR “for an increased 

rate of fire,” but maintained that he “wanted to do it legally.” Id. at 553. Defendant then 

testified that he designed the TCGTR “to contact the trigger group assembly,” though 

ostensibly without disabling the disconnector. Id. at 554. When Defendant began to 

testify about what part of the “trigger group assembly” the TCGTR was designed to 

contact, he asked the court whether he could “show the jury an animation that is on 

YouTube showing how that trigger group works.” Id. at 555. Defendant also offered to 

draw a diagram of the trigger group on a whiteboard. 

The government objected, arguing that the testimony “presents both technical and 

specialized knowledge and under Rule 702 it would be required to come in through a 

qualified expert witness.” Id. The district court sustained the government’s objection 

because it found that Defendant’s testimony concerned “technical and specialized 
6 

knowledge,” id. at 561, but had not been disclosed as required by Federal Rule of 

Criminal Procedure 16. The court acknowledged that Defendant had “the right to present 

a defense,” but noted that Defendant also had “an obligation to follow the rules, the Rules 

of Criminal Procedure.” Id. at 564; accord id. at 572. Defendant concluded his 

testimony and rested his case shortly thereafter. 

The jury returned a guilty verdict on both counts. Defendant was sentenced to 

33 months’ imprisonment, followed by 36 months’ supervised release. Defendant 

timely appealed his convictions.2

 

II 

Defendant argues that the district court erred when it sustained the government’s 

objection to his testimony about how he intended the TCGTR to interact with the AR-15 

trigger mechanism. The district court excluded this testimony after finding that it was 

expert testimony subject to Federal Rule of Evidence 702, but that Defendant had not 

timely disclosed his expert testimony to the government, as required by Federal Rule of 

Criminal Procedure 16. Defendant further argues that the district court’s limitation on his 

testimony violated his Fifth and Sixth Amendment right to present a defense. 

 2

 Defendant also moved for release on bail pending appeal. He argued that this 

appeal raised a substantial question of law likely to result in reversal, namely that 

“the district court violated [his] Fifth Amendment right to testify on his own behalf” 

about his intent when manufacturing the TCGTR. Dkt. No. 10605490 at 7. We 

denied the motion because, even though the district court “would not allow 

[Defendant to] . . . testi[fy] that the trigger system in fact . . . was not a machinegun,” 

“the [district] court permitted [Defendant] to testify about his intent.” Dkt. No. 

10612197 at 2. 
7 

A defendant’s right to present a defense is cabined by the Federal Rules of 

Evidence and Criminal Procedure. 

The Fifth and Sixth Amendments grant a defendant the “right to 

testify, present witnesses in his own defense, and cross-examine 

witnesses against him—often collectively referred to as the right to 

present a defense.” United States v. Markey, 393 F.3d 1132, 1135 

(10th Cir. 2004). But this right is not absolute; a defendant must still 

“abide the rules of evidence and procedure.” United States v. 

Dowlin, 408 F.3d 647, 659 (10th Cir. 2005) . . . . 

In light of the need to satisfy evidentiary requirements, [a 

defendant] bears a two-part burden on [his] constitutional claim. 

First, [he] must demonstrate that the district court abused its

discretion in excluding the evidence. Dowlin, 408 F.3d at 659. 

Second, [he] must demonstrate that the excluded evidence “was of 

such an exculpatory nature that its exclusion affected the trial’s 

outcome.” Id. 

United States v. Tapaha, 891 F.3d 900, 905 (10th Cir. 2018) (brackets and some 

citations omitted). 

When the government disclosed its expert witness prior to trial, it “request[ed] the 

disclosure of Defendant’s experts,” “pursuant to Federal Rule of Criminal Procedure 

16(b)(1)(C).” App. Vol. I at 33. This request triggered Defendant’s obligation to “give 

to the government a written summary of any testimony that [he] intend[ed] to use under 

Rule[] 702.”3

 Fed. R. Crim. P. 16 (b)(1)(C). Defendant did not provide a summary of his 

testimony to the government. Therefore, the district court only erred when excluding a 

 3

 The parties do not discuss whether the government disclosed its expert 

witnesses in response to “[D]efendant[’s] request[ for] disclosure under subdivision 

(a)(1)(G)” of Rule 16. Fed. R. Crim. P. 16(b)(1)(C)(i). Because Defendant does not 

address this point, his only challenge to the applicability of Rule 16(b)(1)(C) turns on 

whether or not his testimony was expert testimony under Rule 702. 
8 

portion of Defendant’s testimony if it was not expert testimony governed by Rule 702.4

 

United States v. Adams, 271 F.3d 1236, 1243 (10th Cir. 2001) (holding that exclusion of 

expert testimony because it was not disclosed to the government in a timely manner was 

an “evidentiary ruling . . . review[ed] for abuse of discretion” even though the defendant 

argued that it denied him the right to present a defense). 

Defendant argues that Rule 702 does not apply because he would have offered 

“lay [testimony] as to the technical aspects and functionalities of [his] device.” Aplt. Br. 

at 20. “A person may testify as a lay witness only if his opinions or inferences do not 

require any specialized knowledge and could be reached by any ordinary person.” United 

States v. Yeley-Davis, 632 F.3d 673, 684 (10th Cir. 2011) (brackets omitted) (quoting 

LifeWise Master Funding v. Telebank, 374 F.3d 917, 929 (10th Cir. 2004)). Lay 

testimony is “not based on scientific, technical, or other specialized knowledge within the 

scope of Rule 702.” Fed. R. Evid. 701(c). “[T]he distinction between lay and expert 

witness testimony is that lay testimony results from a process of reasoning familiar in 

everyday life, while expert testimony results from a process of reasoning which can be 

mastered only by specialists in the field.” Fed. R. Evid. 701 advisory committee’s note to 

2000 amendment (quotation marks omitted). “[P]rototypical examples of [lay testimony 

include] . . . the appearance of persons or things, identity, the manner of conduct, 

 4

 Defendant does not argue that the district court erred by excluding a portion 

of Defendant’s testimony instead of imposing a lesser sanction or granting a 

continuance to allow the government to prepare for Defendant’s testimony. 
9 

competency of a person, degrees of light or darkness, sound, size, weight, [and] 

distance . . . .” Id. (quotation marks and brackets omitted). 

Defendant wanted to testify that he 

designed the kit so that when a notched TCGTR is pushed down by a 

forward moving bolt carrier, it pushes down on the trigger bar 

causing the trigger to move back into its reset position. Because the 

operator is still trying to put pressure on the trigger, the operator will 

pull the trigger almost as soon as it is back in the reset position. The 

TCGTR in this configuration is called a forced reset trigger system, 

otherwise known as a positive reset trigger system. It requires a 

separate trigger pull to fire each round. 

App. Vol. III at 570. Understanding Defendant’s testimony “require[d] . . . specialized 

knowledge” about how an AR-15 works and how its component parts can be manipulated 

to increase the gun’s rate of fire. Yeley-Davis, 632 F.3d at 684 (quoting LifeWise Master 

Funding, 374 F.3d at 929). Moreover, the jury would have needed to understand the 

significance of Defendant’s reference to a “forced reset trigger system” and a “positive 

reset trigger system,” as well as how such systems differ from the analogous system in a 

machinegun. App. Vol. III at 570. This is not knowledge “readily accessible to any 

ordinary person.” Yeley-Davis, 632 F.3d at 684. Therefore, the district court did not 

abuse its discretion when finding that this portion of Defendant’s testimony was expert 

testimony subject to Rule 702. Id. (holding that “testimony concerning how cell phone 

towers operate constituted expert testimony”). 

The fact that Defendant invented the TCGTR does not alter our conclusion that he 

needed to comply with Rule 16’s disclosure requirement. None of the cases cited by 

Defendant hold that an inventor is exempt from Rule 702. Instead, they stand for the 
10 

unremarkable proposition that an inventor may testify as a lay witness and, if properly 

qualified and disclosed, as an expert witness. See, e.g., Verizon Servs. Corp. v. Cox 

Fibernet Va., Inc., 602 F.3d 1325, 1339–40 (Fed. Cir. 2010) (holding that a “district court 

did not abuse its discretion in limiting inventor testimony to factual testimony that did not 

require expert opinion” because the witnesses “had not previously provided expert 

reports or been qualified as . . . expert[s]”). 

Moreover, the district court’s limitation on Defendant’s testimony did not prevent 

him from “directly address[ing a] core issue[ in the case]—his intent.” Aplt. Br. at 24. 

After ruling on the scope of Defendant’s testimony, the district court allowed him to 

continue to present his case to the jury. Defendant concluded his testimony by telling the 

jury the following: 

What would I like you as the jury to know about this kit? I 

guess, again, I would start that I am its creator and I am the 

manufacturer of it. My design for it was completely different than 

what the prosecution has alleged. My intent for it is completely 

different than what the prosecution has alleged. It was intended as 

an educational experience. I designed these kits to fire one round for 

each pull of the trigger, and I sent each one of these kits out in a 

form that they couldn’t do anything to an AR-15, maybe besides 

causing them to jam. I told people not to complete the kit, just use 

the information, the education. Some people chose to complete their 

kit in a way that I did not intend, and a choice that each of them had 

a right to make. Not my choice. 

I will stand here and continue to tell you point-blank, as the 

designer and manufacturer of this kit, that it is my absolute 

100-percent belief that I did not make a machine gun, and that 

because of that I am not guilty of the charges leveled against me by 

the government. 
11 

App. Vol. III at 586–87. Therefore, Defendant was able to testify that he did not 

intend to create a machinegun. The district court’s ruling only prevented him from 

testifying about how the interaction between a TCGTR and an AR-15’s trigger 

mechanism alters an AR-15’s rate of fire. Such testimony might have strengthened 

Defendant’s argument regarding intent, but that does not excuse Defendant from 

complying with Rule 16 before offering expert testimony. Tapaha, 891 F.3d at 905. 

Finally, Defendant argues that he “cannot be foreclosed from” “elicit[ing] 

particularized and technical testimony from lay witnesses”—namely, himself—because 

“[t]he government made the strategic decision to adduce testimony from lay witnesses as 

to the technical aspects and functionalities of” the TCGTR. Aplt. Br. at 20–22. Even if it 

is true that the government improperly elicited expert testimony from lay witnesses, 

Defendant does not raise that alleged error as an issue on appeal. See Fed. R. App. P. 

28(a)(5), (8). Defendant merely uses the alleged error as an excuse for him to disregard 

the Rules of Evidence and Criminal Procedure. But one party’s failure to comply with 

the Rules does not alter the other party’s obligation to follow the Rules. Otherwise, trials 

could rapidly devolve into free-for-alls. As Defendant acknowledged when he asserted 

his right to represent himself at trial, “[t]he right of self-representation is not a license 

. . . . to [disregard] relevant rules of procedural and substantive law.” United States v. 

McKinley, 58 F.3d 1475, 1483 (10th Cir. 1995) (quoting Faretta, 422 U.S. at 834 n.46). 
12 

III 

Defendant also raises three unpreserved issues, which we review for plain error.5

 

To prevail under plain error review, Defendant must satisfy four requirements: 

First, there must be an error that has not been intentionally 

relinquished or abandoned. Second, the error must be plain—that is 

to say, clear or obvious. Third, the error must have affected the 

defendant’s substantial rights, which in the ordinary case means he 

or she must show a reasonable probability that, but for the error, the 

outcome of the proceeding would have been different. Once these 

three conditions have been met, [we] should exercise [our] discretion 

to correct the forfeited error if the error seriously affects the fairness, 

integrity or public reputation of judicial proceedings. 

United States v. Giannukos, 908 F.3d 649, 654 (10th Cir. 2018) (quoting MolinaMartinez v. United States, 136 S. Ct. 1338, 1343 (2016)). 

A 

Defendant argues that the district court erred when instructing the jury on the 

elements of Count 1 of the Indictment, which alleged that Defendant violated 26 U.S.C. 

§ 5861(a) by unlawfully manufacturing machineguns. Specifically, Defendant argues 

that the district court failed to instruct the jury on the requisite mens rea. Section 5861(a) 

makes it “unlawful for any person . . . to engage in business as a manufacturer . . . of . . . 

firearms without having paid the special (occupational) tax . . . or having registered” with 

the federal government. A machinegun is a firearm. 26 U.S.C. § 5845(a). 

 5

 In one footnote, Defendant argues that “the aggregate effect of the errors is 

not harmless” “under a cumulative error analysis.” Aplt. Br. at 46 n. 15. 

Defendant’s brief discussion of this issue is insufficient to garner review on appeal. 

United States v. Cooper, 654 F.3d 1104, 1128 (10th Cir. 2011). 
13 

Instruction Number 13 set out the elements of Count 1: 

1. The defendant was engaged in business as a manufacturer of 

machineguns; 

2. The defendant engaged in such business without having paid the 

special (occupational) tax or having registered as required by federal 

law; and 

3. The defendant knew he was manufacturing machineguns. 

Supp. App. at 15; see also App. Vol. III at 632. “The term ‘machinegun’” was defined in 

Instruction Number 14. Supp. App. at 16. 

Section 5861(a) does not include a mens rea provision. See Staples, 511 U.S. at 

605 (explaining that § 5861(d) “is silent concerning the mens rea required for a 

violation”). In Staples, “the Supreme Court . . . held . . . that the government must prove 

a defendant knew the weapon he possessed had the characteristics which made it a 

statutory firearm” to convict the defendant of violating § 5861(d). United States v. 

Mains, 33 F.3d 1222, 1229 (10th Cir. 1994). We have not previously discussed whether 

the same mens rea requirement applies to a prosecution under § 5861(a). The 

government agrees with Defendant that the mens rea requirement recognized in Staples 

should apply to a prosecution under § 5861(a) because “§ 5861(a) and (d) are structurally 

identical.” Aple. Br. at 45; see also Aplt. Br. at 27 n.8 (asserting same structural 

argument). For the purposes of this appeal, we assume that to be true. 

Defendant’s argument hinges on the third element of Instruction Number 13—

“[t]he defendant knew he was manufacturing machineguns.” Supp. App. at 15. 

Defendant argues that this instruction “did not require the jury to find that [Defendant] 
14 

kn[e]w the specific physical traits that make his device a machinegun,” Aplt. Br. at 37, 

because “[i]t is not clear what word ‘knew’ . . . modifies—‘manufacture’ or 

‘machineguns,’” id. at 39.6

 In Defendant’s view, “[t]he logical and natural interpretation 

of the instruction is that [the] jury need[ed] only find [Defendant] knew he was 

manufacturing something.” Id. The government argues that “knew” modifies 

“manufacturing” and “machineguns.”7

 Aple. Br. at 46–49. 

Defendant is not entitled to relief because any error in the jury instructions was not 

clear or obvious. “An error is plain if it is clear or obvious under current, well-settled 

law. In general, for an error to be contrary to well-settled law, either the Supreme Court 

or this court must have addressed the issue.” United States v. Justice, 679 F.3d 1251, 

1256 (10th Cir. 2012) (quoting United States v. Thornburgh, 645 F.3d 1197, 1208 (10th 

Cir. 2011)). Defendant has not “point[ed] to any authority from this court or the Supreme 

 6

 Defendant argues that the instructions for Count 2, in which Defendant was 

charged with possessing or transferring machineguns in violation of 18 U.S.C. 

§ 922(o), better complies with Staples. With respect to Count 2, the jury was 

instructed that it needed to find that “[D]efendant knew the item he possessed or 

transferred was a machinegun.” Supp. App. at 18. Even if there is a significant 

difference between the instructions for Counts 1 and 2, Defendant has not shown why 

that would affect the outcome of his appeal. The jury convicted Defendant on Count 

2 and we now affirm its finding that Defendant knew the items he possessed or 

transferred were machineguns. Because Defendant manufactured the machineguns 

that he subsequently possessed and transferred, it would have been inconsistent for 

the jury to find that Defendant did not know the items he was manufacturing were 

machineguns. 

7

 This argument is consistent with the government’s position at trial. In its 

closing argument, the government told the jury that, to convict Defendant of count 

one, it needed “to consider . . . whether [Defendant] knew what he was 

manufacturing was a machine gun.” App. Vol. III at 642. 
15 

Court to support []his proposition.”8

 Id. at 1257. To the contrary, we have held that a 

similarly worded instruction complies with Staples and adequately instructs a jury on the 

required mens rea for a § 5861 prosecution. 

In Mains, a defendant was charged with violating 26 U.S.C. § 5861(d) and the jury 

was instructed that it needed to find that “the defendant . . . knowingly possessed a 

shotgun with a barrel length of less than 18 inches or an overall length less than 26 

inches.” 33 F.3d at 1229 (quotation marks and emphasis omitted). We held that this 

instruction, “in accord with Staples, . . . properly required the jury to find [the d]efendant 

knew the particular characteristics which made his sawed-off shotgun a statutory 

firearm.” Id. We reached that conclusion because “the jury was required to find that 

[the d]efendant (1) possessed a sawed-off shotgun with a barrel length of less than 

eighteen inches or an overall length less than twenty-six inches, and (2) knew he 

possessed a sawed-off shotgun with a barrel length of less than eighteen inches or an 

overall length less than twenty-six inches.” Id. Therefore, in Mains, we understood 

 8

 Defendant instead points to a pair of cases from other circuits, only one of 

which concerns a prosecution under § 5861. See United States v. White, 863 F.3d 

784, 786 (8th Cir. 2017) (en banc) (analyzing jury instruction for prosecution under 

§ 5861(d)); United States v. Ahmad, 101 F.3d 386, 389 (5th Cir. 1996) (analyzing 

jury instruction for prosecution under the Clean Water Act). The primary concern in 

White, 863 F.3d at 792, and Ahmad, 101 F.3d at 391, was that the mens rea element 

was contained in its own line of text, and therefore physically separate from the other 

relevant elements of the crime. That problem is not present here. The instruction in 

this case—“[t]he defendant knew he was manufacturing machineguns”—contains the 

mens rea element (“knew”) in the same line as the characteristics of the firearms 

(“machineguns”). Therefore, the cases cited by Defendant do not establish that any 

instructional error was clear or obvious. 
16 

“knowingly” to modify the entire phrase that followed, not just the immediately 

following word.9

 

A plurality of the Supreme Court reached the same conclusion with respect to a 

similar instruction. In Rogers v. United States, a defendant was charged with violating 26 

U.S.C. § 5861(d) and the district court instructed the jury that it needed to find that “the 

[d]efendant knowingly possessed a firearm, as defined” in a previous instruction to 

include a silencer. 522 U.S. 252, 257 (1998) (plurality opinion) (quotation marks 

omitted). After the defendant was convicted, the Supreme Court decided Staples. Id. at 

254 n.1. 

The plurality concluded that, “[s]ince the term ‘firearm’ had been ‘defined above’ 

to include a silencer, that instruction required the jury to determine that the defendant 

knew that the item he possessed was a silencer.” Id. at 257. The plurality “assume[d] 

that the trial judge would have been more explicit in explaining the mens rea element of 

the[] offense[] if Staples had been decided prior to submitting the case to the jury,” but 

was “satisfied that the instructions as given did inform the jurors that they must find that 

the defendant knew that the silencer was in fact a silencer.” Id. at 258. The dissenting 

Justices disagreed, arguing that “[t]he word ‘knowingly’ in the instruction modifies the 

word which follows it, viz., ‘possessed,’ rather than the instruction’s further reference to 

the statutory definition of ‘firearm.’” Id. at 260 (Kennedy, J., dissenting). In closing, the 

 9

 Defendant “does not concede that the Mains instruction suffices under 

Staples.” Aplt. Br. at 41 n.12. But there is nothing for Defendant to concede. In 

Mains, we held that the jury instruction at issue complied with Staples. 33 F.3d at 

1229. 
17 

Rogers plurality cautioned that “[i]t would be wise for trial courts to explain the Staples

requirement more carefully than the instruction used in [Rogers] to foreclose any 

possibility that jurors might interpret the instruction as [the] . . . dissent [did].” Id. at 258 

n.7 (plurality opinion). 

Because of our holding in Mains, any error in Instruction Number 13 was not clear 

or obvious. That being said, we echo the Rogers plurality’s comments about the 

specificity with which a district court should instruct a jury regarding a defendant’s 

knowledge of “the features of his [firearm] that br[ing] it within the scope of the [NFA].” 

Staples, 511 U.S. at 619; see also Pattern Crim. Jury Instr. 10th Cir. § 2.91 (2011 ed. 

2018) (setting out pattern jury instruction for a prosecution under § 5861(d)). 

B. 

Defendant argues that the district court erred in allowing the government to ask 

witnesses to “repeat[] out-of-court statements that ATF believed [Defendant’s] devices 

were illegal.” Aplt. Br. at 31. The government called as witnesses seven people who 

purchased a TCGTR from Defendant. ATF agents visited many of these customers 

during their investigation and told the customers that the TCGTR was illegal. The 

government elicited testimony from four of the customers about the ATF agents’ prior 

statements. Because the government does not dispute that these statements were 

inadmissible hearsay, we assume that the first two requirements of the plain error test are 

satisfied. 
18 

Instead, the government argues that Defendant cannot satisfy his burden under the 

plain error test because the error did not affect his substantial rights.10 We have 

repeatedly held that improperly admitted hearsay testimony is harmless when cumulative 

of properly admitted testimony. United States v. Garcia, 793 F.3d 1194, 1214–15 (10th 

Cir. 2015); United States v. Brooks, 736 F.3d 921, 936 (10th Cir. 2013); see also United 

States v. Martinez, 166 F.3d 1222, at *7 (10th Cir. 1999) (unpublished table decision) 

(collecting cases). Here, the government called ATF Agent Michael Powell to testify at 

length about his expert opinion that the TCGTR was illegal because it was a machinegun. 

Defendant had the opportunity to cross-examine Powell and explore how and why he 

concluded that the TCGTR was illegal. Therefore, because the four brief and conclusory 

hearsay statements admitted through the customer-witnesses were cumulative of Agent 

Powell’s testimony, Defendant has not shown that any error affected his substantial 

rights. 

C. 

Defendant argues that the district court erred by allowing Agent Powell, an expert 

witness for the government, to testify: The TCGTR “meets the statutory definition of a 

machinegun that is found in 26 United States Code Section 5845(b). That definition 

includes any part designed and intended solely and exclusively for use in converting a 

 10 The government also argues that Defendant waived any objection to the 

challenged statements because he cross-examined the witnesses about the ATF’s 

warnings that the TCGTR was illegal. We need not reach the Government’s waiver 

argument because we conclude that any error in admitting the challenged statements 

did not affect Defendant’s substantial rights. 
19 

weapon into a machinegun. This part meets that definition.” Aplt. Br. at 34 (quoting 

App. Vol. III at 469). Defendant argues that this testimony was improper because 

“experts may not opine on ultimate issues of fact without unpacking the technical or 

specialized criteria upon which the opinion is based.”11 Id. at 33. 

“An opinion is not objectionable just because it embraces an ultimate issue.” Fed. 

R. Evid. 704(a). Moreover, “[w]itnesses are permitted to testify about how the law 

applies to a certain set of facts, so long as they provide adequate explanations for their 

conclusions.” United States v. Richter, 796 F.3d 1173, 1196 (10th Cir. 2015). Therefore, 

as long as Agent Powell explained the basis for his opinion, it was not improper for him 

to testify that the TCGTR was a machinegun. United States v. Buchanan, 787 F.2d 477, 

483–84 (10th Cir. 1986) (holding that an expert witness may testify that “a particular 

device . . . must be registered” as a firearm with ATF). 

 11 When later discussing the prejudice he allegedly suffered from Agent 

Powell’s testimony, Defendant also argues that Agent Powell improperly “testified as 

to [Defendant’s] intent.” Aplt. Br. at 45. “In a criminal case, an expert witness must 

not state an opinion about whether the defendant did or did not have a mental state or 

condition that constitutes an element of the crime charged . . . .” Fed. R. Evid. 

704(b). But Agent Powell did not testify that Defendant knew the TCGTR was a 

machinegun when he manufactured the device. Agent Powell testified about his 

examination and testing of the TCGTR, including his opinions concerning the effect 

that a TCGTR has on an AR-15’s rate of fire. Based on his analysis, Agent Powell 

offered his expert opinion that a TCGTR’s only purpose is to convert an AR-15 into a 

machinegun. Consistent with Rule 704(b), the jury was then able to evaluate Agent 

Powell’s testimony when “conclud[ing] or infer[ring] th[at] [D]efendant had the 

requisite mental state” to be convicted of violating § 5861(a) and § 922(o). United 

States v. Archuleta, 737 F.3d 1287, 1297 (10th Cir. 2013) (quoting United States v. 

Goodman, 633 F.3d 963, 970 (10th Cir. 2011)). 
20 

Agent Powell thoroughly explained the factual basis for his opinion that the 

TCGTR is a machinegun. On direct examination, the government asked Agent Powell 

“to explain how [the TCGTR] converts [a] firearm into a machine gun.” App. Vol. III at 

470. Powell then conducted a demonstration for the jury about how the TCGTR worked 

inside an actual AR-15, explaining and showing that the TCGTR would cause multiple 

bullets to be fired without “releasing the trigger.” Id. at 472. Defendant followed up on 

this testimony during cross-examination. In a preface to one of his questions, Defendant 

stated that he understood Powell’s opinion to be that the device “pushes down the 

disconnector which releases the hammer and fires the weapon.” Id. at 486. Powell 

confirmed that Defendant’s understanding was correct, stating: “[T]his device overrides 

the function of the disconnector, which is supposed to prevent you from getting a second 

shot with a single function of the trigger, but this device actually overrides or negates the 

function of the disconnector while the trigger is pulled and the weapon is” firing. Id. 

Powell also testified about why he considered the TCGTR to be a machinegun 

when it was shipped to customers without any of the required bends. He explained that 

the unbent TCGTR was still a machinegun “[b]ecause of the relative ease that it took to 

do those bending operations.” Id. at 474. When a customer purchased an unbent 

TCGTR, they could obtain instructions for how to make the required bends and install the 

TCGTR into an AR-15. It took Powell “approximately five minutes to do the four 

bending operations” needed to complete the device. Id. at 477. As Powell also 

explained, the ease of use did not appear accidental. The “device has to be the perfect 

length in order to function properly in [an AR-15],” “has to be cut to the perfect width,” 
21 

and needs “clearance cuts” or “contouring” “to fit inside of th[e AR-15] without binding 

. . . [and to otherwise] work properly.” Id. at 474. Because Agent Powell adequately 

explained the basis for his opinion that the TCGTR is a machinegun, as defined in 

§ 5845(b), the district court did not err in allowing his testimony. 

IV 

We AFFIRM.