I have a new upper from Palmetto armory and I am having difficulties. It sometimes, not all the time, will not extract a fired round before attempting to chamber the next round. Sometimes it will work fine for 3, 5, or 20 rounds then this issue will occur. I have bought a chamber brush and polished the chamber. I sent it back to Palmetto but they say all is working fine. Palmetto says the issue may be the bolt carrier group but it was purchased from BCM (not the cheap one either). Looking for ideas please.