as far as the taper that i am not sure about that being a problem. my colt and my home brew CAR extract fine--although i did have to play around with the extractor spring pressure on the M-1sales bolt to get it working. oddly the M-1 bolt was backwards in its response to more extractor spring pressure. the more pressure the harder it was to extract rounds.
i have read somewhere that the gas system on the AR when in operation can jam the round deeper into the chamber and cause it to hang in the chamber. this is a slight possibility but i have never experienced a problem--so far.
on thing on examination of AR extractors is that the cut for the rim of the round is much deeper on a 7.62 bolts extractor. which might be why 7.62x39 extractors sometimes fail when combined with an overly strong extractor spring system. YMMV--