Barrel extension scatching case neck

[clutch]

After firing 10 cases out of my new AR15, I noticed two seriously deep parallel scratches in the neck. After a bit of examination I determined that the ejector is pushing the case into the sharp edges of the barrel extension nearest the ejection port.

Now the question, how and with what do I fix this with.

Would a 1/4" round stone work? Like Brownells 657-030-214?

I'm open to other ideas.

Thanks,

Clutch

 

[TCU]

i had the same problem and contacted bushmaster. they wanted me to send in to get worked on and i am a very impatient person and dont like to do extra stuff. I just disassembled it and use a file to clean the burrs on the feed ramp. then i smoothed it with sand paper, using ligher grit each time to get a clean smoothe surface, i cleaned it up good and polished it, i no longer have the problem. It was to the point where when you racked the rounds you had to lock the handle back and hit the release to have enough power to rack it. then when you extracted the round there was 2 big gouges right in it. Hopefully it fixes your problem.

 

[Cemetery21]

It's the inside edges of the barrel extension lugs at the 2:00, 3:00, 4:00 position. They are sometimes sharp and can be gently smoothed with a narrow file or stone. Take care to clean out any filings from the lug recesses and chamber.

 

[clutch]

Thanks for the replies. I ordered a 1/4" diameter x 4" stone from mcmaster.com to fix this. PN# 4451A61 if interested. That looks about perfect for getting into that tight spot. I'll know tomorrow when the stone shows up.

Checking around, I found a use for WD-40, use that with the flex nozzle to flush out the abrasive crud after stoning.

Clutch

 

[clutch]

Stone worked well, I only see light marks now extracting previously fired cases clocked to an unmarked spot. I cycled the brass back and forth against the rub spot to check. Flushed extension with a directed spray of wd-40 followed by blasting a bunch down the barrel to flush followed by time to drip and a few hoppe's saturated patches down the barrel from the breach.

I think I'm good to go now.

Clutch