Problem with AR-10?????

M

msinc

New member
I have an AR-10 308win caliber that developed hard extraction problems after only 25 rounds. The empties are pretty beat up and scratched. When I look in the chamber with a borescope I can see a lot of small pieces of brass "hammered" into the side walls of the chamber. The rifle is equipped with metal magazines {didn't notice what brand} and save for the 25 rounds fired in it is brand new. It is pulling so hard to extract that there are marks on the rim from the extractor itself. Maybe the little pieces of brass junk were in it from the factory but maybe they are getting generated by the cycling of the action somehow. Maybe the rifle needs to be "broken in" but I doubt it. Anyone seen this??? Is it common among the AR-10's to have trouble extracting??? I will say I don't know the history on this rifle but new with 25 rounds down the pipe there is really not much history to it. Any info is greatly appreciated and thanks in advance.
 
I guess the obvious question would be. are you shooting factory or reloaded brass?? The debris in the chamber had to come from somewhere and unless it was left over from test firing by the manufacturer, it would almost have to be from recently trimmed brass that was not chamfered or beveled...

You might chuck the chamber brush in a section of cleaning rod with some lubricant on the brush and use a drill motor to spin the brush in the chamber for about 20-30 seconds in an attempt to knock out the debris that is there....The .308 does develop some serious chamber pressure, but any debris should not have been pressed into the chamber walls....

Anything that decreases the chamber dimensions will cause hard extraction and the scratches on the cases may be the cause of the particles in the chamber from shaving the surfaces, in which case the upper needs to be sent back to the manufacturer for evaluation and correction...
 
Thanks for the reply, sorry I should have cleared it in the first post...yes, this rifle has only ever been shot with factory ammo. I do intend to try polishing the chamber lightly to see if that helps once I wire brush all the junk out. I was thinking maybe the metal magazines were shaving some brass off the cases when they are being cycled. Once I get it cleaned and polished I intend to single hand feed a few rounds and look at the brass. I haven't checked to see if they have burrs or rough spots that could do it. Also, the chamber itself is pretty rough machined. If this were my rifle I think I would probably rebarrel it, but I have seen some pretty rough looking chambers work O.K. otherwise. In fact, if it is minimum headspace I think I might even take a chambering reamer and wisp out a thousandth or two. I doubt it is but I will check it.
 
Maybe over gassing? I have never had an AR-10 currently building one though but my AR-15 had this problem. I bought and adjustable gas block and it fixed the problem. It sounds like the extractor is ripping your casing. I know that sounds to simple but hey you never know.
 
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Sounds over gassed to me. Extraction is really violent and is multiplied with too much gas. Try a adjustabek gas block before touching the chamber.
 
Here is what I found and how it was treated. Test fire was performed and the weapon was found to be "short stroking." It also jammed several times trying to load cartridges into the chamber. The fired empty brass cases showed a lot of scores and scraping from loading and the cycle of the action. Borescope inspection of the chamber revealed brass fragments, both loose and "ironed" on to the walls and in general just a very rough finish to the chamber walls. There was very heavy cut marks from the extractor on the rim of fired cases.
The rifle was cleaned and the chamber polished with Brush Research Manufacturing {BRM} chamber polishing hones both 400 grit and 800 to finish. The headspace was minimum so I was able to polish out just about all of the tooling marks from the chamber. The locking lugs on both the barrel extension and bolt were very rough and I had to deburr and polish them. I verified that the gas port and gas block were in alignment and corrected {radiused} the very sharp edges of the extractor. The rifle was reassembled and test fired and functioned perfectly. The action cycled properly with no jams or glitches and the bolt locked open after the last round like it is supposed to. There are no more scratches or scrapes on the cases. Whether fired or cycled by hand the rifle has stopped damaging the brass.
It is hard to believe this thing was allowed to leave the factory so rough and malfunctioning!!!

Thanks again for your replies and interest in following this repair, and again sorry for the delay...it took a week and a half for the hones to arrive from BRM.

Edit: almost forgot...I did in fact cut two coils off the ejector spring. This rifle was throwing the empties like 12 feet. It also left a slight smear on the brass case head from the ejector plunger.
 


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