Failed bolt extractor in 4 shots - CBC Industries AR-15 16in 7.62x39mm Complete Upper Receiver Rifle Kit

The CBC Upper bolt extractor failed on the 4th round. Optics Planet still has not responded to emails. I contacted CBC Ind. and this is their response, "David, Yes we found out we had a bad batch of extractors come in in our last shipment of 7.62x39 BCG’s. If you want to send it back to me I will get it swapped out for you. I know the steel 7.62x39 rounds are very affordable but we do not warranty steel case ammo being used in our upper as its on our warranty page. The tolerances in the AR platform are tighter than those in the AK platform and the use of steel will mess up the barrel extension and chamber due to the tighter tolerances. If you want to send it back in you can send it to:
CBC Industries". Now CBC acknowledges they have a BCG issue, but I found the info about the steel rounds to be very disappointing. No where on the Optics Planet does it mention the upper cannot handle steel rounds. There was no mention of warranty that arrived in the package. There were also no instructions. CBC response about steel rounds really makes me question the quality of the upper. If the tolerances are that tight, what about 300 blackout of 350 legend those are larger and hotter.