via the supply system same as type 2. CQBR type 3A: Colt-contracted upper, naked without any accessories or buffer supplied. The buffer in the host carbine would be used or upgraded as necessary via the supply system same as type 2. MK18 type 1: NSWC assembled carbine with contracted and/or overhauled parts complete with all accessories to current standards at time of build; will work with H or H2 and could have shipped with either. Units will balance buffer to ammo requirements: H okay with M193 and M855. (All shipboard MK 18s should have H buffers as this was the standard at the time of assembly.) H2 needed for MK 262, MK255 R2LP, or MK 311 R2LP; will still reliably run M193/M855. H3 may be needed for an extreme cases or when the gas port is eroded but the barrel still groups. MK18 type 2: Colt-contracted carbine complete with all accessories (H buffer supplied). Units will balance buffer to ammo requirements same as Mk 18 type 1. MK18 MOD 0 (MK18 MOD O): Designation given to the full rifle, consisting of CQBR upper receiver and M16A1 lower receiver MK18 MOD 1: Similar to the changes found in the SOPMOD Block II kit, the MOD 1 features a gas block end without a front sight and a railed handguard, by Daniel Defense, that extends all the way to the base of the flash hider to provide more accessory rail space for the user. Specifications Upper and lower receivers: The lower receiver is a standard M4A1 lower receiver, sometimes modified with the addition of a CQD RSM sling adapter plate. However, many CQBR rifles also use surplus M16A1 lower receivers. Internally, the CQBR also takes advantage of a larger gas port and modified bolt carrier and buffer assembly. The gas port has been opened to 0.070 in (1.8 mm). A number of Lewis Machine & Tool 10.5" (266.7 mm) upper receivers have also been reported to have been purchased for the CQBR program. These upper receivers feature a gas system optimized for short barrel use. The MOD 1 makes use of a forward sight delete and full-length handguard to provide more rail space for the user. Sights: Initially, detachable carrying handles cut down so that only the rear sight assembly were used. However, most of these have been replaced with the similar, commercially-made Lewis Machine & Tool adjustable rear sight. Also used