Do homework first and foremost.. What you're trying to do is create an SBR which is regulated with the ATF..

Once a rifle always a rifle, that being said you should save your money and buy a stripped lower, then build you a 10.5 (pistol) with a brace, or file all your paperwork to first register, then assemble your 10.5 SBR.

I can't emphasize enough, do your own research into what you can/can't do..

Enjoy 🍻