Production time:  6 months estimated. Complete Aero precision M4E1 upper build Specs: -26.5", 22" or 18" Douglass Premium Handfitted SS barrel 1:7.5 twist 4 groove -Heavy bull profile -Aero VG6 Muzzle Brake 5/8x24 -Aero M4R1 15" handguard -Rifle length gas system -0.936 adjustable gas block -Aero Precision Complete BCG Type II grendel BCG -Aero Charging handle This upper uses a custom handfitted barrel that is chambered and bolt headspaced matched to give the best performance. Our chambers are custom with tighter tolerances and shorter freebore to give the best accuracy. *Some factory ammo may not chamber*