Failure to go into Battery

[BushmasterFanBoy]

This is all happening with one type of ammo right?

Sounds like an ammo issue to me.

Those shorty AR's can be EXTREMELY ammo-sensitive. (AMHIK!)
Even if that ammo had been "fine" until now, it may have been only barely "fine."
Now some little something-of-nothing has changed in the gun, and the ammo is no longer "fine."

One thing is for sure, the barrel IS fine.
5,000 rounds is only a good start.
I would expect at least 40,000 rounds out of any AR barrel that was not a precision match rifle.

First time my gun has run XM, but it has had plenty exposure to full pressure 5.56 before. FWIW, I figured 5k was not even approaching max barrel life.

[W.E.G.]

Not all Federal XM193 is created alike.

See the "XM Fails" thread at Arfcom
http://ar15.com/forums/topic.html?b=...=382153&page=2

[Iraqgunz]

Just stabbing in the dark, since this is long distance diagnosis. Since this is a DI weapon if everything isn't working in harmony I can see where other things would be thrown off. Now I think there was something that I missed. All the ammo involved was the same type and assume the same lot#. I would switch to another type and then see what happens. Then go from there.

I examined my ejector and my chamber thouroghly, no bits of brass in the ejector, and it applies force to an empty case smoothly with no binding. And my chamber is chrome white and smooth. (That didn't keep me from scrubbing it out with a chamber brush anyways)



I'm not sure if that could be a symptom or not, wouldn't gas system wear result in failures like short stroking? Or is there something I don't know about that?

It seems to me that the carbine has enough force to cycle fine, but is lacking enough power to lock the bolt. IIRC in all of my failures the bolt was closed on what was as far as I could tell, pretty much a fully chambered round. It seems odd to me then that the bolt wasn't following suit and fully locking.

Would it sound like a heavier buffer spring could solve that problem?

[Iraqgunz]

BTW- At a particular place that I was working back in the summer of '06 we were using Bushamster carbines. I was asked to do LTI's and repair all missing, damaged or worn items. One of the tasks, involved using a Hawkeye borescope to examine the gas port hole. We had determined that the gas port hole on many carbines was excessively worn and was a cause of some of the issues. IIRC, there was a determination that this was occuring after 7500rounds or so. Of course this was a guesstimate because there was no real way to track round counts.

First time my gun has run XM, but it has had plenty exposure to full pressure 5.56 before. FWIW, I figured 5k was not even approaching max barrel life.

[Ron S.]

5k is the end of a barrels life? I've heard how the AMU guys ditch barrels at insanely low round counts, but IIRC, I thought most barrels will sustain decent accuracy to 10 or more thousand rounds?

Anyways, with this high of a round count, obviously past the break-in period, but well within the life of the upper, should I be looking more at possible broken/failing parts than anything else?

I've done a check on the BCG, my bolt shows no signs of cracks, and my extractor is still good. All my lugs are in perfect shape, and a quick inspection of my barrel extension/upper shows nothing out of the ordinary.

Is there a possibility this could be ammo related? This failure has been non-existant since I began to shoot this batch of XM193-A. I've shot 5.56 pressure ammo before just fine, for larger round counts in more compact times as well.

Yeah, chromed lined barrels will start to open up around 5k, SS around 4k. By "the end of a barrel's life", I'm not saying you won't be able to hit a guy. I'm saying if you ever shoot competitions (not the ones running around shooting at mass targets), you'll be dismayed by the accuracy from there on out. Your groups just open up more and more after that. Sure, you'll still be able to smack someone down at 10k rounds, but you won't be winning any award. It's just a matter of how picky you are, and what kind of accuracy you want.