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Posted: 5/8/2011 8:25:44 PM EDT
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Hey Y'all,
Need some thoughts from the assembled wisdom. I have been shooting the hell out of my Aug A3. Over 1500 rounds with no indepth cleaning, no lube... 2 carbine classes worth. Some total of maintenance was wiping down the bolt and the exterior. Finally had my first failures yesterday. They were definately "you're dead" jams. After over 1500 rounds of xm193, I switched to some HSM 556. 2 first round fired, and the rear third of the case extracted. The front 2 thirds remained in the chamber. The following cartridge fed into the chamber. It was lodged tight. Unclearable jam. Fortunately the Aug design made it pretty easy to clear. I pulled the barrel, and pulled the round, and the front 2 thirds of the shell casing from the chamber. I ran a chamber brush through the chamber and fired 42 more rounds of xm193 with no failures. Sooo... here is what I am thinking... The xm193 has an annealed casing. THe HSM doesn't. The chamber was likely dirty from heavy use. The XM193 continued to function, and the weaker commercial brass was ripped apart by the extraction. Sound theory? What say you all? Pics to follow. Damien |
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I have seen this failure with the AUG platform before. with the MSAR's it was a case of a poorly honed, or not honed at all, chamber. Since you had a good amount of trouble free rounds on it, I would say it is the HSM ammo.
But youre right, it is easier to clear on the AUG than an AR....that said, youre still dead. |
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Yeah, I'd never use HSM for anything other than shooting paper and steel on the range.
I'm wondering if the Aug has an unusually violent extratction. I was training with some guys from a local PD swat team and they use HSM as training ammo all the time. Never had an issue in their M4s. D |
It's the XM193 ammo that's the problem.
Not my photo but that is what happens when I run XM193 through my MSAR. It only happens once or twice during a carbine competition but I will no longer use XM193 when I run out of the stuff. From now on I will only use PMC Bronze ammo or Hornady. 
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Was the HSM assembled on once fired brass? If it is fairly thin brass to begin with and fired in a semi-auto it'll get some stretch right above the area where the case gets thicker just above the base. HSM might size to the low end and you could have a chamber on the generous end of spec. Brass stretches again at the thinnest portion and is yanked by the extractor... Case head seperation.
Lotsa variables involved here. |
| Sounds like an ammo problem for sure. If you are trying to do a scientific test of how many rounds fired before failure you need to use the same factory ammo and not change it. But since it ran 1500 rounds without fail, then as soon as you switch ammo it jams imeaditly, then you switch back and it runs 42 rounds perfect. So that just tells me that other ammo is bad, not the guns fault. |
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Quoted:
I'm just thinking outloud but could it be a gas timing issue. I've read that if the pistion moves too soon, the brass case has not depressurized enough to allow extraction. This has caused the bolt to either rip off the rim or tear the case in half. Your assertion is spot on. When your extractor starts ripping case heads off you can always look to a timing issue on a piston gun. You are absolutely correct in asserting the bolt is traveling to the rear prior to the pressure in the chamber lowering enough for the case to be extracted easily. Now here is a thought for you... when my STG-556 was doing this I sent it back to MSAR and the remedy was to open up the hole in the front gas selector a bit. I am guessing the fouling has reduced the size of the hole on your AUG. Remember, that little hole is the RELIEF hole. Any gas that doesn't go out that little hole slams the piston home. Soak that little sucker in some Mpro7 and use a wire brush on it and see if your problem doesn't go away. |
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For what its worth, I found Militec lubricant has excellent properties for the gas plug and piston. With heat, it impregnates the metal making it more slick even when dry. This has helped my piston stay cleaner and easier to clean up after shooting. Great stuff.
PS if it is a timing issue, your extractor won't last very long. |
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Quoted:
It's the XM193 ammo that's the problem. http://i371.photobucket.com/albums/oo157/Furyataurus/casefailure2.jpg Not my photo but that is what happens when I run XM193 through my MSAR. It only happens once or twice during a carbine competition but I will no longer use XM193 when I run out of the stuff. From now on I will only use PMC Bronze ammo or Hornady. That was Ultramax ammo in that picture... 
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Quoted:
Did the failure you are talking about look similar to this...? http://img224.imageshack.us/img224/4812/malf7lj.jpg http://img224.imageshack.us/img224/9093/malf11sm.jpg http://img204.imageshack.us/img204/8646/malf23iy.jpg i was shooting my A3 with wolf ammo yesterday and it did exactly this 2x.....is that the ammo? gun was fairly clean & I had put aprox 100 rounds through gun since last cleaning i was thinking it might of had something to do with the ammo |
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Anyone checking headspace?
That's where case head separation occurs with excessive headspace. A new gun shouldn't have that problem. Dirty gas relief ports are another possiblity. Wolf shoots really dirty in my rifles and fouls the chamber badly. I'm going to have to check my A3's headspace. |
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Well in my layman understanding annealing is so that you get brass to soften and can form it to be more homogeneous so I would think that since we know the XM193 is annealed it's probably going to chamber and extract better than the HSM 556.
So while with the XM193 you may not have noticed any issue with the dirty chamber the HSM 556 really didn't like the chamber dirty. So yeah, in my humble rank amateur ammo connoisseur opinion your theory seems pretty darn sound. Now keep your rifle maintained. 
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The failure I posted pictures of above was commercially reloaded ammo that was using once (or more) fired military brass. Probably fired through a SAW with loose headspace...
At least in my case, I would attribute it to faulty brass rather than to the weapon itself. If it happens with new ammo or happens repeatedly, I would be looking closely at headspace or some other issue... |
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