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Posted: 3/22/2012 3:22:14 PM EDT
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I have a CMMG MK3 with a Rainer arms barrel that fails to eject some ammo and I cant figure out why. I bought it used but unfired, and have since shot about 70 rds through it.
Winchester whitebox 308 seems to fail to eject about 1/3 of the time. USA Ammo (Re-man with LC brass) fails to eject about half the time. But....Privi functions 100% so far, i think Ive shot about 30 or 40 rds of it. I bought a Slash heavy buffer and spring and it made no difference in performance. 
rifle 
typical malfunction....it doesnt eject the spent case and instead slams it forward along with the live round. 
Last rd in the mag...it locked the bolt back but didnt kick out the case. I dont get it. Any ideas how to make it run 100% with all ammo? |
Stop using Winchester white box and USA Ammo.  Seriously, WWB has a rep for being underpowered. And in my experience most reloads are as well. Most likely for liability reasons. I shot DAG and Port surplus as well as 100 rounds of Hungarian steel case MWS I believe. Everything functioned 100%. Try something known to be loaded hotter. Privi is excellent ammo for blasting. Maybe some of the Federal soft points from WM. My .02 ETA: 70 rounds is still a very small amount to break in a new rifle. Try sticking to the hotter loads for a while. After you hit 500 rounds then you can try the WWB again and see what happens. I have had rifles give me all kinds of trouble when new, then after running a case of ammo through them everything starts to function better. |
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Check if your ejector has sufficient tension on it as well.
I don't believe in "breaking-in" a rifle. I expect them to run from the get go. All mine do if built right, and properly lubed. I don't have experience with the ammo in question, as I only shoot hand-loads through my AR10's. A gas gun runs optimally with a certain load, bullet weight, and brass dimensions. Rules of the road. |
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Use a good quality grease on the carrier, bolt, and receiver.
A light coat will improve the cycling and help with your ejection problem. I found that using oil was not enough for a 308 gas gun. I agree that gas guns like specific loads, that is why an adjustable gas block is advised for 308s. You can fine tune the gun to the loads you like. |
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Quoted:
Use a good quality grease on the carrier, bolt, and receiver. A light coat will improve the cycling and help with your ejection problem. I found that using oil was not enough for a 308 gas gun. I agree that gas guns like specific loads, that is why an adjustable gas block is advised for 308s. You can fine tune the gun to the loads you like. I used LSA, what kind of grease should I use? |
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Whether or not it's short stroking is not the problem. You should be able to have the empties eject all on their own.
To me, it looks like either a very weak extractor spring (dropped extraction) and/or a weak ejector spring. This looks like a bolt problem, not a gas system problem. |
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Quoted:
Whether or not it's short stroking is not the problem. You should be able to have the empties eject all on their own. To me, it looks like either a very weak extractor spring (dropped extraction) and/or a weak ejector spring. This looks like a bolt problem, not a gas system problem. Thats what I thought at first but then why can I shoot a full mag full of Privi and then have problems with winchester and LC brass? I just dont get that. You could be right, but I dont understand what then would make the privi brass work 100% of the time as opposed to other stuff. |
| It could be how the tail of the round is formed by each manufacture. Your extractor may simply not like certain profiles, thicknesses, metallurgy. Trying a new extractor might be worth a go, yours might be out of spec. If the rounds that do eject have a decent amount of force, which looking at your brass deflector it looks like they do, i would rule out the ejector. |
| Sinnerman is correct. If it will lock the bolt back on last round then it is not underpowered ammo. If a gun is short stroking, then a heavy buffer and spring is opposite of what you need. Like Sinnerman is saying, if the end of the case clears the chamber, it should eject, whether it goes back enough to strip the next round or not. |
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Quoted:
Whether or not it's short stroking is not the problem. You should be able to have the empties eject all on their own. To me, it looks like either a very weak extractor spring (dropped extraction) and/or a weak ejector spring. This looks like a bolt problem, not a gas system problem. +1. Classic failure to extract/eject. Google or search in here "failure to extract" or "double feed" (although the experts will flame your butt off if you claim that's a double feed lol). Example: http://www.ar15.com/archive/topic.html?b=3&f=118&t=443919 . Every time I've encountered this it was a weak extraction issue, cured completely with using the BCM Crane O-ring kit and in one case my extractor/pin fit was all bound up and too tight. |
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ok, could be a few different things. First, I would like to know where the rounds that do eject, land, both the winchester and privi? This will give an idea on the gas. Second, press in the ejector with your thumb/nail, is it really strong? Third, look at the extractor, is there anything in there, is it rough, are you leaving extractor marks on the rim of your brass?
you could have a problem with the ejector, extractor, and gasing for the weight of your buffer/spring. Go with a CS flat wire spring to start, but sounds like it could be two problems, since the privi ejects all the time, I would like to know where the brass lands and check for extractor and if there are ejector swipe marks on the base of the brass. Look for signs on the Winchester brass also, need more info. In your picture it looks like the round came out of the extractor, but didn't get pushed enough by the ejector. So check your ejector tension and then see how much tension is on the extractor? |
| i'll bet its the extractor - take the bolt in your hand and snap a case into it. if you can still push the extractor a little tighter onto the rim you found your problem. rip out old stuff, use a new pin make sure extractor rocks full range without grittiness binding, etc - make sure dont scuff up and gall the pin when you put it in. throw away the springs you have, get the crane kit and use the o-ring, the spring, and the little rubber inside plug. remove clean and inspect the ejector while you are at it. lube the shit out it with mobil 1 and that could solve it all. it did for me. my extractor was binding up a little in comb with weak single spring and it just wasn't gripping the rim that last little bit, causing it to let go some times right after firing and the case would not eject and would just ride down with the next round being stripped off the mag. just my 2c. hope this helps. |
| you have a point the cmmg might be different i have no idea about cmmg/sr25 parts interchangeability - i suggest getting a fresh correct new extractor (and ejector while your at it) spring from cmmg, buy the bcm o-ring kit and try the o-ring and plug on the cmmg spring just to be safe. |
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Barrel Length? Gas System Length? Gas port size?
Check carrier gas key bolts, ensure tightened securely. Check gas rings, ensure all three slots are set at least 90* past each other. Try a new gas tube with current gas block. Try a new gas block with current gas tube. Try a new gas tube and new gas block. |
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pretty sure as I stated above it is either ejector or extractor, I would focus on the extractor. What happened in your picture above is the extractor let loose of the rim, the extractor should have held it while the ejector pushed it out.
Take the bolt apart, alot of video's online how to do it. The extractor is easy, just punch out the pin. The ejector you have to push in to relieve tension from the spring so you can push/punch out the pin. Check both before you check. Usually ejectors are too strong, but they do get crap in them that makes them not work correctly. Even if the ejector was working correctly, the extract should have held on to the case and it should have been stick out of the side. |
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Ejector spring and/or ejector. This would be the first thing I would look at, followed by the extractor. I don't see it being a gas related problem.
The .308 AR's need a lot more lube than the little sisters. Some light grease on the bolt is also a good thing. Tetra grease or Lubraplate 135A on the bolt rails. |
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