The Gemtech Suppressed Bolt Carrier is a drop-in replacement and will allow the shooter to choose between suppressed (S) and unsuppressed (U) settings without any permanent modifications to the firearm. No longer will you need to change gas blocks, buffers, or any other components. Not only that, but with the Gemtech Suppressed Bolt Carrier, there is a reduction in carrier speed and less felt recoil, bringing the cyclic rate of the suppressed rifle down to unsuppressed levels. The carrier is designed to operate with full power 5.56 and 300 BLK ammunition and will not cycle with subsonic ammo. While it can be used for subsonic 300 BLK, more reliable cycling is had in the unsuppressed setting while using subsonic 300 BLK ammo. The 14.5" Colt M4 has a 25% decrease in carrier velocity while suppressed. 10.5" Daniel Defense MK18 has a 16% decrease in carrier velocity while suppressed. Features Reduce Bolt/Carrier speed while suppressed (S-setting) Unsuppressed velocity is unchanged (U-setting) from that of a normal bolt carrier Reduces Felt Recoil Reduced Blowback to shooters face Less wear and tear on weapon system