I was at a gun show last weekend and looking at a few AR pistols. I'd love to build one and add that Sig Sauer SB15 arm brace. Not to use it as intended, but as a butt stock.

It seems like it would work well after trying it on a couple of pistols at the gun show **and is ATF approved. You could have a fun little SBR without the tax stamp and its completely legal.**

Yeap. Thats plan A then after I move to a free state I will pay the tax for the SBR and a suppressor.

Still on the wall with the barrel length. 7 or 9....I want to go 7.

But the performance out of a 9 inch barrel is tempting.

Barrel Cartridge Velocity Energy

9 in (230 mm) barrel 300 AAC Blackout, 115 gr UMC 2,120 ft/s (650 m/s) 1,136 ft·lbf (1,540 J)

16 in (410 mm) barrel 300 AAC Blackout, 115 gr UMC 2,295 ft/s (700 m/s) 1,344 ft·lbf (1,822 J)

9 in (230 mm) barrel 300 AAC Blackout, 125 gr OTM 2,030 ft/s (620 m/s) 1,143 ft·lbf (1,550 J)

16 in (410 mm) barrel 300 AAC Blackout, 125 gr OTM 2,215 ft/s (675 m/s) 1,360 ft·lbf (1,840 J)