I know what the catastrophic result would be, damage to the barrel, upper and lower receivers, and the bolt carrier group.  As the title says, what is the average malfunction when headspace becomes excessive?  Does it have light primer hits or does the firing pin pierce the primer, ya know things like that.  

To quote TonyRumore:

"Excessive headspace will not cause a catastrophic failure in an AR. I have tested it throughly. The case will split in half right in the middle on every shot, but nothing will let go.

If you haven't tested it yourself.......you are just repeating what you have overheard.................

Tony Rumore"

That's certainly interesting.

I'd suspect accuracy would drop off quite a bit too.

I know I'm surfing through older posts but this topic brought up a rifle I once worked on.  The closest thing I'd seen to catastrophic failure in an AR type rifle (this particular one was an M16A2).  

I was visiting an Army friend at his arms room and he pulled this rifle out of a rack, he could not seperate the upper and lower because someone had reassembled it without the recoil spring and the bolt carrier was stuck in the buffer tube.  I removed the buffer tube and continued to disassemble the rifle and was shocked to find so much damage.  (the rifle was not fired without the spring, it was reassembled without it after the damage had occured)

Let me list the damage first (I wish I had a camera to document the damage more thoroughly).

*The cam pin was sheared in half.  It broke at the weakest point, the hole for the firing pin.
*The bolt carrier had damage to the cam pin slot, towards the rear, not towards the front.  
*The charging handle was Fubar'd at the gas key end.
*The firing pin was present, but I don't remember any damage to it.
*The barrel was straight (visually), I did not see any bulges but I don't remember removing the handgaurds either.
*The gas key was damaged as well.  The portion just above the cam pin was bent.  Most likely once the cam pin broke and was making it's way out of the bolt carrier, it contacted and moved the forward portion of the gas key out of the way.  The forward portion was bent upwards.
*The upper receiver was intact, the cam pin recess (space in upper for cam pin when bolt rotates to locked position) was not too bad.
*The cam pin slot along the inside, roof of the upper had the anno scraped off but was not grossly out of shape.  Finish could have been scraped off from manual (by hand) movement of the bolt carrier post damage, then again maybe not.

Since I was just a visiting "civilian", I didn't put any gauges through it.  No one seems to know the exact cause.  I have a few theories.  I have a pretty good handle on how the damage happened but I have two theories on what caused the situation leading up to the damage (the root cause).

So the question to those that know the AR's better than they know their spouse is this:
>What events must take place to snap the cam pin.  Remember that the damage to the cam pin slot in the bolt carrier was towards the rear, not the front of the slot.  

Hints:

1.  In relation to the bolt carrier, what position was the bolt in for the cam pin to absorb the force of the round firing.
2.  How does the weapon fire in the position described in hint #1?
3.  Pull your BC/B out and look at it.  Now consider hint #1.

I have seen barrels blown out from flub rounds followed by live rounds (blocked barrel), I don't think this was the case with this one.  If you're going to mention Headspace, you'd better list exactly how HS is involved (if at all).

If this doesn't pull the countertop gunsmiths out of the kitchen, nothing will.

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