The Mat9 Upper is a self-contained complete 9mm receiver. Bufferless, compact and reliable. The blowback system runs suppressed or unsuppressed without spring changes. The charging handle is non-reciprocating and reversable for right or left-handed shooters. It is compatible with AR9's and AR15's with Mag Adapters. Compatible with Glock, Sig, Colt, Scorpion and Mp5 magazines. Veteran Owned made in San Antonio! Bufferless, self contained system AR lower compatible Blowback Design Non-reciprocating steel charging handle 4140 Nitrided steel bolt and action parts 6061-T6 anodized upper receiver 4150 Lightweight Nitrided Barrel, 7.825" long, 1:10 twist, 1/2x28 threads Tapered Mfg: Matador Arms