I have a 10.5" 5.56 SBR upper and enjoy it quite a bit. The 10.5" barrel still gives you good velocity and that plus flash cone makes it no more a nuisance to shoot than a 16" barrel (at least IMO). I'm thinking about getting a 9mm upper and magwell conversion as well. This will most likely be a range toy so the magwell conversion will be for Glock mags since I already have an abundance of them. I'm looking for opinions on barrel length and manufacturer. I have seen videos of people shooting 4" barrels with a 6" handguard and it looks super fun. PSA seems to put these together for a good price. Also, can I run a stock buffer setup? Thanks!