My M4 seems to be pushing BB's too far into the chamber.. If the hop-up is turned down too much (to the point that .28's don't arc up, not all the way off), BB's fall out of the barrel when pointed down, or fire out of the gun at a severely reduced (read: useless) speed. This is using a Modify VSR bucking (
http://www.wgcshop.com/wgc2008/main/...fy&catid=&cat=), not sure if that has any bearing on it.