The extractor should have the internal piece (buffer), since it just keeps the spring from collapsing sideways over time.


As for double feed, is spent case left in the chamber, and the live round is being shoved into the back of it/ spent case still in the action, and live round being feed out of the mag jamming on it.

Or is the problem two live round of mag during the feed instead.


If spent case is being left in the chamber, then either rough chamber, extractor spring or extractor not hanging onto the rim of the spent case during the pull, or rig just way over gassed, and bolt unlocking too soon for a clean pull of the spent case (residual bore pressure too high and pressure welding the case to the chamber walls for the extractor to be able to pull it cleanly.


If problem is the spent case is pulled out of the chamber, but is not clearing the action, then either extractor problems again, with the extractor not hanging onto the the spent case rim all the way back to back of stroke, or could be that the bolt face is retracting back past the back of ejection window on the stroke, and as the spent case is trying to pivot off the bolt face, tagging the inside/back edge of the ejection port window to defect the case back in.  The check the stroke length, pull all the way back on the charging handle, and the front face of the bolt should stop 1/8"~1/4" in front of the back edge of the ejection port window, and the last inch pull of the charging handle should be the same tension as the middle of the pull.


As for two live rounds out of the mag, with the spent case clear of the action before the bolt goes to strip a round on the way back forward, that one is a mag problem for the most part.  If cheap clone mags are in play, then could be a bit of over jolt of the buffer off the back of the receiver at back of stroke, but this jolting is going to be the semi norm for a pistol rig build.  To check mags, fully load them one round short, then rasp the bottom of the mag off something solid to jolt the mag.  If the rounds come fountain spraying out on the jolt, the mag is shite to begin with.

Lastly, if you had/paid a gun smith build the rig, then hand it back to him to correct it.  Just because someone can assembly a AR from parts, does not make them a gun smith, but instead a parts assembler/ changer at best.  An AR gun smith will know the needed parts needed for the specific build, and how to check the parts during the build, to make sure it going to run correctly once it has been built.