APFSDS
NES Member
So now that I have my brace I'm trying to narrow down an upper, x39? 5.56, 300aac? 9mm? and length I'm learning towards 10.5" no matter the caliber, I do already have a slick side 300 but since I don't reload an x39 seems like a way to leverage 30cal for the cheap. unfortunately Brandon has made that as expensive as 5.56
The first SBR AR upper I had was a 7" 9mm with a mag conversion block. In my opinion a dedicated PCC lower is the way to go if you want one, but I found that a 10.5" 5.56 with LWRC UCIW stock is almost as small and weighs about the same, plus it uses regular mags. At the time I built it you basically had to use 50 dollar colt SMG mags if you wanted a PCC. The 7" did suppress well with 147 grain ammo and was lighter than my 5.56 rifle + heavier rifle can. A 12.5" 5.56 will still supposedly launch XM193 fast enough for it to fragment out to about 50 or 100 yards, but a 10.5" does not get it fast enough to fragment at all, if memory serves. Note that any short barrel is going to be plenty loud using full power rifle ammo, especially with a brake. I have only fired a handful of unsuppressed shots out of my 12.5" as it has a big ol' brake mount that will detach your retinas and singe your eyebrows. The 10.5" is noticeably louder and flash-ier than a 16" even with just an A2; the original XM118 had a moderator so the NVA/VC couldn't tell the report from a normal M16. I have a KVP linear comp that takes the edge off and was only about 40 bucks.