Cracked Upper

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Cracked Upper

Postby Shermanator » Tue Apr 01, 2014 7:49 am

So this happend sometime during my last two range trips. I noticed it yesterday while cleaning it. The crack in the upper is just below the ejection port cover, see pictures below. My guess for the round count is somewhere around 15-20K mostly on full auto.

Upper is a MGI Quick Change Barrel upper.

So after looking at the pictures is this considered normal wear and tear? The crack does go completely through.

Image

A closer look
Image
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Re: Cracked Upper

Postby clash14 » Tue Apr 01, 2014 8:28 am

I have nothing, that sucks though. Certainly cant be normal. Is that even a high stress area of the receier?

Nothing extraordinary about that trip to the range as far as conditions and use are concerned?
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Re: Cracked Upper

Postby Rattler » Tue Apr 01, 2014 8:59 am

It clearly took some undue stress. Ever have an out of chamber discharge or anything?
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Re: Cracked Upper

Postby Shermanator » Tue Apr 01, 2014 12:02 pm

The metal below the crack seems very thin and flimsy. No Out of Chamber discharges I'm aware of.
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Re: Cracked Upper

Postby clash14 » Tue Apr 01, 2014 12:16 pm

I think you just amswered your own question! Structural stresses from high volume firing found their way to the weakest place.
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Re: Cracked Upper

Postby Rattler » Wed Apr 02, 2014 8:18 am

There shouldn't be any stresses there though. Nothing to speak of anyway. I wonder if the datum was just off a little bit when the forging was machined and the whole machining process is a little off center making thew walls on the right side by the ejection port thinner than they should be. I've seen that before.
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Re: Cracked Upper

Postby Shermanator » Sat Apr 26, 2014 5:30 pm

Well got a new upper from a different manufacturer and the thickness was probably double or more on both sides compared to the one that cracked.
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Re: Cracked Upper

Postby John A. » Sun Apr 27, 2014 6:03 pm

I agree with the other guys.

That's not really a high stress or high wear area.

High stress area would be barrel threads/trunion and the lugs.

High wear area would be the bolt rails and charging handle channel.

What's the crack on the outside look like?

Has someone maybe dropped it or dropped something on it? If so and it was enough to crack it, it would've left some kind of mark. Not just a crack.

If no OOB discharge, what about any blown primers? Squibs?

I'm just grasping at straws to think of something that could cause a crack (which considering the location could only be pressure from something other than normal activity), but the most obvious would be the thin wall and if it's that thin, we all know it's not right. Do you have a caliper that you could measure it with? I'll measure a bunch of mine if you need a comparison.

I have dpms slickside extruded aluminum upper, a dsa, an oly, another dsa, and something or another else.
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Re: Cracked Upper

Postby Shermanator » Mon Apr 28, 2014 6:12 am

Well as I said my carrier key on the bolt was loose too. So it might have been something to do with that. I can't measure the upper as I have thrown it away. It wasn't cracked from being dropped or something dropped on it. The crack went completely through but the more jagged areas were from the inside, so it was caused from the inside going out.
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Re: Cracked Upper

Postby Rattler » Mon Apr 28, 2014 6:24 am

Certainly something nefarious happened somewhere along the line. Not pointing fingers of fault at all - but perhaps if the gas pressure was enough that was leaking off your carrier key, but that would have caused cycling issues too. Oh, well. Guess we'll never know.
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Re: Cracked Upper

Postby John A. » Mon Apr 28, 2014 7:17 am

I'm sorry that it happened and you had to toss it, but I am thankful that you noticed it and it didn't cause any real damage to anything or anyone.

I am doubtful that the gas key being a little loose did that. The crack was not really in the same general area as the key and was located pretty low on the receiver.

I know that pressure can do some strange things sometimes, but like water, it usually finds the easiest (or weakest) way out, which in this instance seems that it would have been out the ejection port or magwell, or seam between the upper/lower, etc.

Most times when a KB happens, the mag is blown out and the upper swells in that general area.

After sleeping on it, I don't want to place blame, but I would be looking at the specs of the upper itself at this point, but that is just speculation on my behalf.

I'm not sure what the expected life span is of a receiver itself, but I know that you can wear out at least one or two barrels in the time it takes to wear out a receiver itself. Matter of fact, I'm sure you know of many transferable M16's that have been around since the 70's that are still putting right along, so 20,000 definitely sounds like a very short lifespan.
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