CMMG MK4 HT 22 AR15 UPPER RECEIVER – the CMMG MK4 HT dedicated .22 LR AR15 FLATTOP UPPER RECEIVER lets you do live-fire training with affordable rimfire ammo while retaining the weight, balance, and feel of your rifle. Replace your existing upper with the AR22, load the included Black Dog .22 LR magazine, and you’re ready to shoot. You practice with your existing trigger and fire control components, so the trigger pull feels the same. The mil-spec receiver has a standard MIL-STD 1913 Picatinny rail, charging handle, forward assist (non-functioning), and ejection port cover. Inside, the standard bolt/carrier assembly is replaced by a dedicated “bolt rail” of hardened tool steel with a blowback operated stainless steel bolt inside. Both components are built to run hard and handle the abuse of long practice sessions. M4 has the appearance and weight of a USGI M4 upper, with correct contour barrel, standard M4 handguard, A2-type flash hider, and a gas block/front sight tower with bayonet lug, sling loop, and square front sight post.