personally, i think that bolts are just plain more rugged and reliable. way less moving parts to freeze up, and try to clean mud out of, etc. you have to think about this from the standpoint of running through muddy, half frozen swamps, snow, freezing rain, sand, etc., etc.. all thiose small working parts, that work fine in your sporting firearm, are actually a liability in a service rifle. how they ever made automatics that work under those conditions baffles me. i guess they beef up the parts, and fit them loose.