I have quite a few AR. 20", 16", 10.5", and in between in 5.56. 14.5" pinned and welded in 308. 9.5" in 300 blk. 4" in 9mm. And I have a lonely SBA3 brace that needs a pistol built around it. I'm probably looking at something in the "not completely practical" category but not quite as far out there as a 2" barrel (see picture). I've considered a 7.5" in 5.56 or a 12.5" in 308. And I'm trying to avoid any niche calibers. If it's going to be a range gun, I'd prefer not to build something that'll cost me $1.50 every time I pull the trigger. Expensive ammo takes the fun out of a fun gun. Does anyone have any interesting ideas?