So, I've decided to build an Ar. The eventual goal would be to build a reliable duty rifle and I really would like it to be a SBR. As far as the upper and lower go, I'm looking at a Mega Arms monolithic railed carbine upper and a matching billet lower. As far as the barrel length goes this is pretty much the style/design I'm looking for, with the Noveske KX3, to help keep some of the muzzle blast directed forward. Here's a picture of the Mega monolithic upper I'm looking at. I don't know if this is a hot topic here or not, but I can't decide between gas piston or direct impingement. This rifle will be used by me as a patrol officer, so the advantage of keeping the rifle cooler during sustained fire is a moot point. I'm not overseas fighting a war, so I don't expect to be firing through 6-8 or more mags. God willing. Suggestions on this issue are great. Barrel? I don't know. I think an 11.5" length would be as short as I want to go giving a total length with the Noveske KX3 of 14.25 inches, roughly. This is what my PD issues, and it's a handy rifle. I would like to keep mine a similar length. So, right now I'm just brainstorming and any advice is welcome. Thanks guys.