Why rifle safety features are important - AI-AW50

A couple other SnipersHide members and I went out Sunday morning for some extreme long range shooting. There were two AI-AW's present: a GAP-barreled .260, and a factory .308; one AWSM in .338LM, and one AW50. The wind was real bad, but we were able to put a bunch of hits on a target WAY out there - we estimate 1600 or 1700 yards based on the dope we needed to apply to hit it.

We were shooting some 750gr AMAXs through the AW50...



... and at some point noticed this ...



Hmm, that's the pressure release "valve" (really a plastic disk) that covers the two vents from the bolt area. The AW50 has one such vent on either side of the receiver to safely vent pressure away from the shooter if there is a case rupture. Hey, wait, did that just fall out or something? Weird.

Well I was convinced that it couldn't have just fallen out, so I started to look through the fired brass and here's what I found:




So there was a gross defect in one of the LC cases. At some point we shot that round and didn't notice anything different - except it was almost certainly one of the "misses" - and kept shooting. Neither the shooter or observers noticed anything different at the time, nor did it affect the ability to make hits after the bad round (maybe 5 or 10 more rounds were shot until we noticed).

Being able to take a ruptured case head while igniting over 230gr of powder, make the condition safe for the shooter and not even noticeable at the time, and continue shooting accurately is a very strong testament to the engineering and design that went into this gun. In a lesser gun, this failure could have caused serious injuries and rendered the rifle inoperative.

When we went over the footage later, we actually found the footage of the bad round:

http://www.youtube.com/watch?v=257Du_JrCGg

And the obligatory "group" photo

You can see it in the first two photos.

Hi,

The LC cases were supposed to be once fired when I got them, and none of those had been fired more than once by me since then - so this case had either one or two firings only. It was "over 230gr", so one can probably guess what load data I was using for match reloads.

I say it's a gross defect because of the failure it caused and the history of the cases. The best explanation I can offer is that there was a weak spot in the brass due to some unknown factor. I do not believe the brass was worked excessively based on its history. I think I will cut the brass open to see if I can determine anything else about it.

Yes, all the red ones are that.

No kidding. I am good about inspecting brass while prepping it so I am pretty sure there was no visible indication of this weak point.

I believe it's just to keep stuff out of the action, since it opens to where the back of the barrel meets the front rim of the bolt. Also, in conjunction with the safety ports themselves, their absence indicates something bad happened. Per AINA's insistence, I will be sending the rifle to them so they can check all the parts exposed to gas for potential gas erosion. I would be very very surprised if anything needed to be fixed.

I don't know if they call it a valve or a port or what -- I've never seen an official parts diagram.

Hi,

I don't know the ultimate origin of this piece of brass. I prefer to use either brand new brass or once-fired brass that has been fired in something other than a MG-- however, at the time I loaded this ammo I had some LC ready to go. If I come across a case that does not easily full size, I throw it out. From now on, I may use *only* brass in those preferred categories and sell off the LC. Who knows. We'll see how it cleans up.

Looking at the case in person, I don't see stretch marks that are very out of the ordinary for cases fired in a bolt gun. I do see a ring at the top of the web where the body of the case has expanded to fit the chamber, then tapering down as the web thickens.

What I find interesting about the external appearance of the rupture itself is the powder pattern. In the quoted photo, just under the (C), there is no powder fouling trace for about half the length of the slit. It looks like the gas flowed mostly clockwise out this slit, at least opposite the spot lacking fouling.

Anyway, I hope to find out more when I section the case.

Thinking about what 1858 wrote about hoop stress, I wonder if the web area was either undersized (and thus had less chamber support) or was weak in this case (or in this area) for some reason, ie, a defect.

I'll post more as I find out more about both the case itself and any effects AINA finds in the rifle. They did tell me that another rifle had something similar happen using c.a. 1950's brass and it toasted the chamber.

Now, where can I get a .416 barrel for my rifle... I know all that brass is new.

-z