I have a Bushmaster XM15 E2MS, it is a A3 flat top with a 20 in bbl, and I have been having problems with it short stroking. After the charging handle is pulled all the way back and dropped, a round is chambered, then it fires fine. The bolt carrier goes back and the shell is ejected. However, the bolt carrier doesnt go back far enough to get behind the next round in the magazine and chamber it. So consequently the bolt slides back forward without the next round.

I have tried many different types of ammunition(handloads, factory loads, 45gn, 55gn, 68gn,ect) I have also tried different magazines and replaced the gas tube and I have still been having the same issue. It has also been cleaned and lubed(not over lubed though) and I have still been having the same issue. Does any one have any ideas or suggestions for me?

I tried to give as many details as possible but if you have any other questions feel free to ask.

Thanks