This is how 27 C.F.R. ?479 (e.g. NFA) defines pistol:
Pistol. 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).

So, you all are living in a "technical loophole" that doesn't ACTUALLY exist in reality, no different than declaring the fact that an individual's birthday is unknown somehow exempts statutory crimes against that same person.

An AR-15 pistol has one grip - in front of the stock, oops, I mean "uh, Arm Brace" , and the addition of a vertical grip would require the use of two hands to fire it, since any hand on the vertical grip cannot reach the fire control components.

OOOOPS. That's wha I'm talking 'bout.

*MIC DROP*
By this standard, any handgun that is sold today is in violation of that rule because since the advent of Jeff Cooper and The Modern Technique, no one outside of bullseye shooters uses a one-handed grip when shooting a pistol, and the companies that make these guns know that.