View Full Version : Unusual Extractor Marks On Brass...What To Do?
July 11, 2012, 08:27 PM
I have a brand new AR Bolt Carrier Group, with 80 rounds so far, that is leaving two distinct divots at the base of the brass on the rim near the primer. The tiny chips in the brass are in two places 180 degrees apart. I assume this is from the extractor and I have never had this happen with any other BCG. I normally would not be too anal about this happening except I plan to re-load with this brass and buffing the base of each case to re-load is a step I'd rather not do in the long run. Is this just a overly strong extractor that will mellow out after use of does it sound like something else? Thanks...
July 12, 2012, 04:05 AM
hard to say for sure without pics,but i would closely examine the boltface,extractor/ejector for burrs/sharp edges.
July 12, 2012, 04:55 AM
Could be happening during feeding
July 12, 2012, 05:44 AM
What jbrown said. Look for imperfections on the bolt face, ejector and extractor.
Run 100rds of steel case then check with brass case again, that may "wear in" the bolt face.
July 12, 2012, 07:21 AM
I have a brand new AR Bolt Carrier Group, with 80 rounds so far, that is leaving two distinct divots at the base of the brass on the rim near the primer. The tiny chips in the brass are in two places 180 degrees apart
180 degrees apart means they are on opposite sides of the brass. (360 is all the way around, 180 is half of that, so one on each side)
The extractor is only on one side. I would think with the extractor they would be less than 60 degrees apart, both on the same side.
They are also next to the primer, the extractor doesn't touch there (or shouldn't:D).
Can you take a fresh round and cycle it in by hand (pointed in a safe direction) and then ease it out of the chamber while watching to see what is touching it?
I have seen a bad/frozen extractor leave big gouges on the bullet side of the rim. But the gun wouldn't extract right most of the time. (The ejector couldn't kick it out)
You don't feel anything out of the ordinary on the bolt face do you? Does the extractor move freely or is is "crunchy"?
July 12, 2012, 08:26 AM
I took out a 35 power hand lens to look real close at the base of these spent shells and indeed it is the face of the extractor lip shaving small pieces of brass as the bullet exits the bolt face and is then leaving a "tit" of brass near the rim. Upon close inspection the scuffed up area on the brass is the same width as the movable lip of the extractor. I took the BCG apart last night and noticed that the extractor spring had the aftermarket o-ring installed around the spring so I removed it and will see if the unit does the same today. I gather that the extractor needs to be worn in a bit, with such a tight spring/o-ring set up, so it does not chew on the brass as the case is dismounted from the bolt face. If it quits raining today I'll run some rounds through the rifle and see what happens.
PS- Added a picture below but my camera does not do close ups so I had to photoshop a bit. Note the extractor scrape on the edge of both shell lips facing you at the 6 o'clock position and also the round tit formed above the above the casing lip. Then note the smaller brass tits formed on the opposite side at about the 11:30 position from your standpoint.
July 12, 2012, 09:02 AM
I have never used the O-ring.
I have read, however, that it can cause too much extractor tension.
Maybe this is the case?
I think trying it without is a good idea.
I thought that the extractor was smaller, but I don't have my rifle here in front of me to check though.
Does the extractor feel crunchy or odd when it moves?
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