they are very cheap to buy and make the gun smoother to shoot.
instead of the blow back action on the bolt slamming into a metal cross bolt it hits the rubber instead.
we all know that rubber is softer then metal, so instead of a 'clang' you get a nice rubber bounce.
for the $5 or $10 that the bolt buffers cost they really are a very easy upgrade.
that said ive switched all of my bolt buffers over to the Kidd ones because they are so easy to get in and out compared to all the others.
the upgraded Kidd ones, not the pure rubber ones, the one with the metal inner bolt and the rubber outer sleeve.