Whether you want the smoothest shooting carbine possible or are looking for added reliability while shooting hotter loads or suppressors, CMMG's Action Tuning Kit gives you the added flexibility to make your CMMG perform exactly how you like it. This optional Action Tuning Kit allows you to adjust the action to your preference much like changing buffers or changing gas port settings on an adjustable gas block. Small, Medium, and Large weights allow for you to test and find the right weight for your setup. There is no universal answer for which works best. Barrel length, ammo selection, and suppressed or not play a large role in determining your weight. Currently can be used in any of the CMMG Radial Delayed Blowback platforms, as well as Mk47 and MkW-15's that have the .250a ^2 roll pin hole on the tail of the carrier.Included:Small, Medium, and Large weights(3) .250a ^2 x .625a ^2 roll pins