Complete Bolt Carrier Assembly With Jpbc-7 Large Frame Variable Mass Carrier, Jpeb-308 Jp Enhanced Bolt, Jp Enhanced Cam Pin, Firing Pin, And Jp Firing Pin Retaining Pin. Will Also Work In DPMS LR-308 And Will Only Work With Armalite If Used As A Complete Bolt Carrier Group BCG Assembly. Parts Do Not Interchange With Armalite. (This Item Must Be Used In Combination Of A JP Silent Captured Spring System.)