Just got a new Bushmaster carbine (14.5 in. barrel.) It's my third AR. This one is having reliability issues. Problem is probably an extraction problem. I'm getting the bolt back with a loaded round under the spent casing problem. During the first 50 rounds this happened about every 3rd or 4th shot. Disassembly, break-in, lubrication on ejector, etc. has gotten the problem to once every 50 shots. This isn't a cleaning or lube problem. My feeling is that the extractor just occasionally lets go of the case when it's about 95% extracted, then moves forward, stripping off a fresh round. Would a Wolf replacement extractor spring help? Could this be a break-in issue. Only have about 150 rounds through it. (Previous AR's were very reliable from the time they were new.) Would a new Colt carbine extractor fit my Bushmaster carbine? Thanks in advance for any help. All rounds were Winchester 55 grain white box.