Quote History Quoted:
My first guess would be one of two things:
1. Wrong buffer
2. Wrong buffer spring.
Or, a combo of both.
If you're not seeing fouling outside the gas block and you've checked alignment, doubtful that's the culprit.
View Quote
Buffer and spring are an easy check, and just need to pull all the way back on the charging handle, to make sure that bolt face stops 1/4~1/8" in front of the back edge of the ejection port window, and that during the pull, the tension on the CH stays the same from half way back, to all the way back.
If buffer was too long, receiver extension too short, then bolt face will not make it back this far, and if spring is too long, then going to coil bind out before bolt face gets this far back.
As for spring tension, if super sonic loads are in play, then could be too weak, and the bolt unlocking too fast. In cases like this, then look at the spent case rim, since bolt unlock too soon as spent case is pressure welded to chamber walls, will cause the extractor to bend the hell out of the rim backwards on the pull.
If ammo is loaded to too high of working pressure, or problem with leade too short and bullet embeding into rifling on loading, then spent primer is going to be flowed way too close to sides of brass primer rim pocket to show the signs of over pressure their instead.
So really, all points back to the gas system on the upper, with either leaks, or blockages with items not aligned to begin with. If those can be weeded out as not the problem, then it time to pull the upper apart, to check the gas port size.
And again, with none pistol length gas port location, rig has to be set up for the ammo in play to begin with (sub sonic or sonic ammo).