Drop-in replacement for standard buffer and spring Reduce felt recoil Keep the buffer spring from rubbing against the inner wall of the buffer tube Buffer mass is designed to stay under constant tension against the bolt carrier Rubber O-ring on the head of the buffer mass prevents metal on metal contact Made in the U.S.A. Lifetime Warranty. Compatible w/ AR15 with carbine-length buffer tubeAR10 version is available please find under AR10 parts. The SRS comes with Red LOCTITE on the front metal stop and Blue LOCTITE for the bottom bumper when reassembling we recommend reapplying LOCTITE. The SRS can be installed with or without a buffer retainer. The polymer bumper goes towards the rear of the firearm and the weight mass with the o-ring goes towards the bolt carrier.