On a quality AR15 or its variations the bolt is cut in a way that the cam pin can only be inserted in one direction, the proper one needed for the rifle to function correctly.
In the case of this DPMS .308, it was not cut that way. The owner of it dutifully took apart and cleaned his bolt carrier group after each range session, and finally accidentally installed the bolt in turned 180 degrees. When he fired the first shot, the rifle attempted to eject the case into the side of the upper receiver and the rifle jammed. In this particular case, I had an awkward time getting that spent case out of his rifle.
And on a side note, use quality ammunition. Poor quality reloads or defective/damaged rounds can cause catastrophic results.
Your .50 BMG rounds should not do this when fired.