The CMMG Mk3 Gun builders kit includes most of the necessary parts to build up your lower group except the commonly upgraded parts. Does not include Fire Control Group, and pistol grip. Compatible with CMMG Mk3 Lowers and most LR308 type lowers. Please note that not all 308 lowers are the same. The CMMG MK3 lower parts kit is designed to work with CMMG lowers, and are "Mil-Spec". This parts kit is not compatible with PSA PA-10 lower receivers.