My understanding is that the brace must be fully collapsed. Yours is not. Again. I would. Not. Post. This.
Again, it needs to be over 26" with the brace collapsed.
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Under Federal law, a “handgun” means “a firearm which has a short stock and is designed to be held and fired by the use of a single hand….” 18 U.S.C. § 921(a)(29). Under an implementing regulation of the National Firearms Act (“NFA”), 27 C.F.R. § 479.11, a “pistol” is defined as:
A weapon originally designed, made, and intended to fire a projectile (bullet) from one or more barrels when held in one hand, and having (a) a chamber(s) as an integral part(s) of, or permanently aligned with, the bore(s); and (b) a short stock designed to be gripped by one hand and at an angle to and extending below the line of the bore(s).
The NFA defines the term “firearm” to include, among other things, an “any other weapon, as defined in subsection (e).” Id. The NFA defines the term “any other weapon” (“AOW”) as:
… any weapon or device capable of being concealed on the person from which a shot can be discharged through the energy of an explosive, a pistol or revolver having a barrel with a smooth bore designed or redesigned to fire a fixed shotgun shell, weapons with combination shotgun and rifle barrels 12 inches or more, less than 18 inches in length, from which only a single discharge can be made from either barrel without manual reloading, and shall include any such weapon which may be readily restored to fire. Such term shall not include a pistol or a revolver having a rifled bore, or rifled bores, or weapons designed, made, or intended to be fired from the shoulder and not capable of firing fixed ammunition.
26 U.S.C. § 5845(e); see also 27 C.F.R. § 479.11. Importantly, pistols are excluded within the definition of an AOW.
The ATF has long held that by installing a vertical gore grip on a handgun or pistol, the handgun or pistol is no longer designed to be held and fired by the use of a single hand. As a result, it no longer qualifies as a handgun or pistol under Federal statutes and regulations. Additionally, since it is no longer a handgun or pistol, it is not exempt from being classified as an AOW. Therefore, if an individual installs a vertical fore grip onto a handgun or pistol, he or she is “making” a firearm under the NFA, specifically, an AOW. Under the NFA, the term “make” includes “manufacturing, putting together, altering, any combination of these, or producing a firearm.” 26 U.S.C. § 5845(i).
On June 25, 2019, the ATF clarified its position regarding how overall length for firearms using stabilizing braces should be measured. If the stabilizing brace is stationary, only standard receiver extensions are considered in overall length measurements. For example, accessories (extensions) that have superfluous material are not included in the overall length measurement. However, when a device operating as a stabilizing brace is attached to a firearm using a folding or collapsing mechanism, overall length is measured with the brace in the folded or collapsed position. Otherwise, a firearm could avoid classification as an AOW, yet retain the concealability and functionality of an AOW.
Summary
Pistols are not regulated by the NFA. Pistols are excluded from the definition of AOW.
If you add a fore grip to a pistol, the ATF no longer classifies it as a pistol. It becomes an AOW, which is regulated by the NFA.
If the overall length of the firearm is 26 inches or more, it is not “capable of being concealed on the person.” If you add a fore grip to the firearm, it does not become an AOW, nor is it regulated by the NFA. However, if you conceal it on your person, it becomes an AOW, which is regulated by the NFA.
Muzzle devices are not included in overall length. Only standard receiver extensions are considered in overall length measurements. If the firearm is equipped with a stabilizing brace and a folding or collapsing adapter, overall length is measured with the brace in the folded or collapsed position.
It is illegal to make or possess unregistered AOWs. If you want to add a vertical fore grip to your pistol, file an ATF Form 1 application to register it as an AOW, or better yet, an SBR.
I'll edit to add - you can do whatever you want. I have over a dozen tax stamps. I've been doing this for a long time. I know the laws and don't get anywhere near the lines. I have a TS clearance and cannot afford to fuck up. I know a lot of people #YOLO and do whatever they want because they know the chance of getting convicted by the ATF for some dumb shit like a foregrip is close to zero. But those people aren't posting stuff on the internet.