Built exclusively for Primary Arms. The FM Products blast diffuser extends past the 5.5” M-LOK handguard and directs all the excess gas and concussion of your shots forward instead of the sides, making this much more enjoyable to shoot at indoor ranges. The upper and lower receivers are machined from billet aluminum allowing for a greater degree of customizability for look and function. The magazine well and upper receiver feed ramps have been machined for use with Glock magazines, yet it is still compatible with standard AR-15 parts like a trigger, pistol grip, and safety selector.