Clayton, the buffer tube must have been omitted to get around the National Firearms Act prohibitions. These AR pistols are typically built, not bought.

If the gun is incapable of firing semi-automatic, doesn’t have a buttstock, etc, it does not fall under the legal definition of a “short-barreled rifle”, which would require one to jump through the ATF’s legal hoops and pay a $200 tax stamp. Also according to the ATF, the receiver must be certified by the manufacturer as never having been assembled into a rifle. If it ever had a rifle barrel attached to it, even if it was never sold or used, the receiver is considered as being part of a rifle, and subsequently changing it into a pistol configuration makes the result fall under the definition of a short-barreled rifle.

Regardless, an AR pistol is kinda dumb, really. The ONLY thing .223 (5.56mm) ammo has going for it is velocity. With such a short barrel, you get only a fraction of the velocity and power, as well as accordingly less accuracy and range. Without a long barrel to be propelled through, .223 is not much more than a .22 round.

A charging handle was attached along the top of the receiver. The internals have clearly been modified.

It does seem it would have to be a shorter bolt carrier assembly, possibly for .22