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.

[Hoser]

Too much gas or a rough chamber.

[TheBelly]

Too much gas or a rough chamber.

this drives a couple possible fixes: adjustable gas block and/or cleaning up the chamber. a band aid for the overgassing is a heavier buffer, although it's still an overgassed gun.

if you're not comfortable diagnosing those yourself, there's plenty of folks who can make recommendations as to who their favorite 'gun plumber' is.

[DenverGP]

Well, slight edit to the original post. 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. Had it happen 3 times in about 20 rounds. And the unfired case dropped right out when I pointed the gun up. So maybe the extractor isn't grabbing the rounds right?

As for the over-gassed option, it is not an adjustable gas block (no adjustments I can see on the gas block), so I assume that would mean a trip back to the manufacturer to correct?

As for rough chamber, newbie looking by eye I can't see anything, and I could't find any scratches on any of the cases that would indicate an issue.

[Tim K]

Try another BCG if you have one.

[brutal]

In the pics, the brass looks pretty roughed up.

[ray1970]

My guess is probably an out of spec extractor. I imagine it isn't engaging the case rim good. Could be a rough chamber but since you say the empties come out easy I would probably feel comfortable ruling that out if it looks OK on a visual inspection.

[TheBelly]

Not to be contrary, Ray, but the body of the brass in the pictures looks pretty rough.

OP: you dint need to send it all the way back to the manf for a gas block. There are several local/semi-local folks that will do it for you for a good price.

[DenverGP]

body of the brass in the pictures looks pretty rough.

I'll try to get some side by side shots of unfired and one of the jammed cases. Looking at a spent case and a new unfired round out of the box, I don't see much difference, and thats with my bright work-lamp and reading glasses on. My camera tends to really exaggerate any surfaces too. something about the macro setting.

you dint need to send it all the way back to the manf for a gas block. There are several local/semi-local folks that will do it for you for a good price.

I'll see what the manf has to say, and then look into my options. Would it need an adjustable gas block? Or can the gas block just be drilled with a smaller hole to reduce the gas?

I have done a little digging learning more about similar issues, and more about the ar parts in general.

I checked my extractor, it has a spring and an o-ring, but I see a lot of comments that the o-ring is only needed if the extractor isn't firm enough to start with, and some comments that suggest on a carbine length system shouldn't be needed.

Also, noticed my BCG is a "full auto" or "m16" cut, where the top and bottom of the tail are cut to the same length. I saw some comments that the m16 cut can help since it increases the weight of the bcg, giving pressure a little more time before it tries to extract the round.

[Great-Kazoo]

Not to be contrary, Ray, but the body of the brass in the pictures looks pretty rough.

OP: you dint need to send it all the way back to the manf for a gas block. There are several local/semi-local folks that will do it for you for a good price.

It's Plan B. However on any new firearm, the mfg should handle the problem. Why pay out of pocket? Granted it would be quicker. Myself i'd polish that chamber then road test it. OR try some Federal or other brass stuff.