FTE issue

[DenverGP]

Got a new AR yesterday from Kentucky Gun Company. Rifle is made by Xtreme Machining http://www.kygunco.com/xtm-ar-15-rif...on-stock-81426 Very basic, but does have melonite barrel.

Got it home yesterday, Separated the upper and lower, removed the bcg and charging handle, cleaned and lubed up the bcg and bolt, ran a brush and a couple patches down the barrel. Cycling by hand, everything seems smooth.

Took it to the range today, first 5 rounds ran great, then on the 6th round had a Failure to extract. The case tapped out easily with a cleaning rod, just barely tapped on the case to knock it out. The extractor had ripped the rim off the case.


Checked to make sure nothing obvious in the chamber, bolt carrier group looked good. Reloaded the rifle and the same thing happened again. The next 4 or 5 rounds all failed the same way. I removed the BCG, got out my chamber brush, cleaned it a little, put a little lube on the brush and ran it around the chamber, then ran a patch down the barrel.


Next 5 rounds ran good, then the same failure to extract for the next 5 rounds before I stopped for the day.


All cases that had FTE had the rim under the extractor either damaged or completely ripped off. Even rounds that extracted correctly show a little damage on the rim.

EDIT:
I was able to reproduce this with a full mag inserted, and just cycling the rounds by pulling the charging handle and letting it drop and chamber the next round. I think I just didn't try enough times.

Ammo used was new commercial PPU 55 grain .223 rounds.


I've got an email into the manufacturer, but any suggestions on things I should check?

I inspected the fired cases, no signs of over-pressure, primers all look normal, cases don't look unusual except the damaged rim.

The ppu fired cases from my rifle all measured at .376 at the bottom of the case just above the rim. Some other 223 cases (not mine) I collected at the range measured .373 at the same point.

The ppu fired cases all measured right at 1.760 length. The other cases I found were all around 1.740-1.755.

Some pics of the damaged rims, and several pics of all sides of one of the damaged cases.