The measurement is from the rear of the buffer tube to the tip of the barrel without the muzzle device (or with, if pin and weld).
That’s also a pistol brace, not a stock at all, and it doesn’t screw on it slips over the buffer tube. The buffer tube is screwed into the lower and held on by a properly torqued castle nut and an endplate that is (hopefully) properly staked, but being that those are essential for the function of the firearm (while the brace and muzzle device are not), that is the measurement the ATF uses.
If it’s an SBR he should put a stock on it, but since it has a pistol brace I’m betting he hasn’t filed for a tax stamp on it yet, other than the can of course.
The measurement is from the rear of the buffer tube to the tip of the barrel without the muzzle device (or with, if pin and weld).
That’s also a pistol brace, not a stock at all, and it doesn’t screw on it slips over the buffer tube. The buffer tube is screwed into the lower and held on by a properly torqued castle nut and an endplate that is (hopefully) properly staked, but being that those are essential for the function of the firearm (while the brace and muzzle device are not), that is the measurement the ATF uses.
If it’s an SBR he should put a stock on it, but since it has a pistol brace I’m betting he hasn’t filed for a tax stamp on it yet, other than the can of course.