ar15pinnedmag

Hey guys, I've built a few ar15's now. With the prevelance of the rifle there are a ton of fixed mag options that make reloading a fixed Mag at the range pretty easy. Problem is I'm building a 9MM AR rifle now and there are zero products like a comp mag, BF-10, Mean Arms or anything of the...

Can I have a pistol grip, adjustable stock and a muzzle device if the magazine is pinned? Was told yes by a few people but cant find the law.