i recently put together an AR-15 in the last year. i used all dpms components, upper, lower and buttstock etc. i did install a chip mckormick trigger. when i took it to the range, however the rifle would only cycle black hills ammo of 60 grains or higher. i've tried all other types of ammo and the problem is the same: the bolt doesn't travel back far enough to load the next round. i've checked the alignment of the gas block, checked the rings on the bolt, degreased the bolt and bolt carrier. has this happened to anyone or does anybody have any ideas about this? i would appreciate your input very much.