Flat-top receiver with 12-inch barrel and carbine-length A2-type handguard. 1:20 twist rate. Direct impingement operating system. Complete upper receiver comes with 49/64-20 TPI threaded muzzle. This upper receiver assembly is intended for use with a registered SBR or class III lower receiver. This unit is 100% complete and is compatible with any standard-specification lower receiver (no modifications required). All NFA rules apply. Threaded muzzle devices are optional and must be selected as an upgrade option. Ships with one 7-round magazine. Weight of upper is 4.3 lbs.