AR15 Lower Parts Kits. Sort By: Quick view Out of stock. BCM. BCMGUNFIGHTER™ AR-15 Enhanced Lower Parts Kit - Black. MSRP: $130.00 Your Price: $119 ... When You assemble the Lower Receiver with the parts included in the kit, this will be a fully functional rifle. Until then this is not an operational firearm. As of May of 1986 there can be no new machine guns made for the civilian population. M16 parts, hammers, triggers, sear, sear pins and bolt carriers are available as replacement parts.