Magazines can be done by the conversion inserts (EndoMags) or by an adapter. The basic one is the Colt style adapter for Colt (Uzi magazines with a cut for the release) magazines. I have that in one SBR and a Stern Glock adapter in another. I did the Glock magazine first, since that is what I’m issued (Glock 19) and the SBR is integrally suppressed.
For the buffer, you really can’t run a standard buffer setup in a blowback 9mm. First, the 9mm bolt doesn’t have a separate bolt from the carrier. The “carrier” is the bolt. Due to that, the standard AR buffer system length is too long that causes a few problems. 9mm buffers usually are longer… or you can put an insert to take up the difference.
Blowback buffers are also heavier. My two 9mm SBR buffers are in the 9 to 11 ounce range. I go heavier since I tend to shoot both suppressed (as mentioned earlier, one is integrally suppressed). The weight of the bolt (which has a weight in the rear) and buffer are what keeps the action closed until pressure drops to a safer level. Standard carbine buffer likely will allow the bolt to open prior to that… which you don’t want to occur.
