30-06 case separation with M1 Garand

[sofbak]

I actually just read an article on the Garand in Handloader over the break. See if this bit makes sense to you: long cases can also contribute.


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I agree with all the slamfire scenarios in that book page, except one. I'm not sure how excessive head space could cause a slam fire. But the others are possible.

The problem I have with any of those scenarios is that they don't lead to or contribute to a case head separation event. In those described events, the gun simply fires a fully chambered cartridge without pulling the trigger, and the action would function normally unless there were other problems present.

The geometry between the back of the bolt, the firing pin, and the hammer prevent the hammer from contacting the firing pin unless the bolt is closed (not necessarily fully rotated into the receiver). Additionally there is a small bridge across the walls of the receiver at the rear of the bolt, that prevents the firing pin from being moved forward until the bolt is fully rotated into battery. It's called the safety bridge, and unless it is worn (some do, I've had a couple of Garands that didn't pass the safety bridge gauge test) it won't allow the firing pin to contact the primer.

Now, with more info from the OP, that being the cracked stock, I'm more convinced the gun fired out of battery. Usually cracks like that show up from firing an overcharged round, and the bolt travels backwards with excessive kinetic energy, slamming hard into the back of the receiver. The receiver transmits a lot of that energy into the stock, and...."crack!"

But even an over charge doesn't necessarily produce just a severed case head. But it could have been an overcharge that was just enough to cause the described damage without grenading the whole gun. IDK.

I still postulate that it was an out of battery discharge, and since the bolt was not properly rotated and secured in the receiver by the lugs, it came back against the heel of the receiver with a lot more energy than normal. And the case head sep occurred because the portion of the case not supported by the chamber wall got no backup for the 60ksi pressure the cartridge produced when fired. Thus it was sheared off where it was close to the end of the chamber.

Too bad op couldn't find that case head. A measurement of the diameter at the open end might have given more info on the nature of the failure.

[bigbossman]

I am going to reinspect all my 30-06 under a magnifying glass.

No need to. Straighten a paper clip, bend one end 1/4" up 90 degrees and file to a point. Run it inside the case, and rake it up on the inside wall. If incipient separation is imminent, the point will snag in the internal groove.

I check ALL my fired centerfire rifle brass this way, before processing.

https://aussiehunter.org/cartridge-case-head-separation/

[croue]

[divingin]

OP - on the lower set of cases, does the right hand most case look like the rim is bent? Or is that just an optical delusion.

All of the "lower" cases in the bottom row look like a wider extractor groove. I'd assume it's a lighting thing.

Case head separation is usually caused by pushing the shoulder too far back when sizing (this assumes nothing in the firing goes wrong like an out of battery ignition.) On firing, the pin pushes the cartridge against the shoulder of the chamber, pressure ramps up and the case holds itself there (due to pressure), and the unsupported case head blows back against the breech, stretching the case. Depending on how much the shoulder is pushed back, and how stout the load used is, it can show up after one firing, or take several firings before it becomes obvious.

All bets are off if the case was fired in an obviously incorrectly locked up condition though.

Any chance you can measure the difference from base to shoulder between a fired case and one of your unfired reloads? Shouldn't be more than a 2 or 3 thousandths difference.

[sofbak]

Maybe the author of that book was trying to describe a case with a datum length that was longer than spec. I. E. the shoulder wasn't "bumbed" back enough (queing Guffey in 3, 2, 1.....).

But even so, if the bolt doesn't fully close, it can't rotate into battery, and the safety bridge is supposed to retain the firing pin and prevent it from contacting the primer-even if the pin was long enough to reach the primer in that position, until the bolt is rotated into battery. Additionally if the bolt doesn't fully close, then the hammer isn't supposed to be able to contact the firing pin either. I suppose if you had a really, really worn down gun, it is possible.

But in the OPs event, the gun discharged when he slapped the op rod forward. That is the key element that tells me this event wasn't a conventional slamfire, and the gun fired out of battery by a stuck/jammed firing pin.

A genuine anomaly!

[sofbak]

All of the "lower" cases in the bottom row look like a wider extractor groove. I'd assume it's a lighting thing.

Case head separation is usually caused by pushing the shoulder too far back when sizing (this assumes nothing in the firing goes wrong like an out of battery ignition.) On firing, the pin pushes the cartridge against the shoulder of the chamber, pressure ramps up and the case holds itself there (due to pressure), and the unsupported case head blows back against the breech, stretching the case. Depending on how much the shoulder is pushed back, and how stout the load used is, it can show up after one firing, or take several firings before it becomes obvious.

All bets are off if the case was fired in an obviously incorrectly locked up condition though.

Any chance you can measure the difference from base to shoulder between a fired case and one of your unfired reloads? Shouldn't be more than a 2 or 3 thousandths difference.

Thank you for the explanation. I can see how a short case could separate like that. And I can see how pressure escaping out the breech could cause both the damage to the OP's bolt, and could have caused the cracks in his stock.

But how do we connect this to the event that detonate the cartridge? That being the slap to the op rod handle that supposedly fired the gun.

I can't connect all these dots with one line. It could be that there were two different conditions present, 1) a short case that resulted in the case head sep, and 2) some other out of spec condition of his gun that caused it to fire when he bumped the op rod (?).

[smoothy8500]

2) some other out of spec condition of his gun that caused it to fire when he bumped the op rod (?).

Trigger sear/disconnector or hammer hooks are possible culprit. Sounds like the hammer followed the bolt and fired the round.

[Ranchogunner]

I agree with this being an out of battery firing. That's what it felt like. So what you are saying, and others too, in simple terms, is the bolt/firing pin mechanism failed to function normally, setting off the round before it was "locked" in the chamber, causing the bolt to be pushed back with extreme pressure, sending the bolt parts flying. And those actions are responsible for the head of the case being torn off. I think that is the most likely scenario.

I just had an ejector break on a lever action rifle, so any part or assemblage of parts on any gun can fail at any time.

[Ranchogunner]

Thank you for the explanation. I can see how a short case could separate like that. And I can see how pressure escaping out the breech could cause both the damage to the OP's bolt, and could have caused the cracks in his stock.

But how do we connect this to the event that detonate the cartridge? That being the slap to the op rod handle that supposedly fired the gun.

I can't connect all these dots with one line. It could be that there were two different conditions present, 1) a short case that resulted in the case head sep, and 2) some other out of spec condition of his gun that caused it to fire when he bumped the op rod (?).

The slap on the op rod handle is just the normal way to release the bolt on the Garand to catch a round and chamber it. I have done that hundreds of times. Sometimes it releases by itself, and you got to be quick to get your thumb out of there. If you don't, you might get a case of "Garand thumb"

So a malfunctioning bolt/firing pin would set off the round before it was fully chambered. That's got to be what happened.

[bigbossman]

Trigger sear/disconnector or hammer hooks are possible culprit. Sounds like the hammer followed the bolt and fired the round.

I'd check the hammer hooks. Any chance someone did a trigger job? If so, maybe the hooks are not filed correctly.

[Ranchogunner]

I just tried that with 3 live rounds and they all slide in nice, but the head on all sticks out of the chamber about 1/8 inch. I think that is normal. They fit nicely and flush into my L.E. Wilson case gauge, which is the standard that I use. I am going to fix up a couple of dummy rounds to test in my other Garand which is functioning fine, and close the bolt on it (not ready to do slam the bolt on live ammo after that incident). I will get back to you later.

As far as how many times I have reloaded the brass -- about 3 or 4 times.

[sofbak]

The slap on the op rod handle is just the normal way to release the bolt on the Garand to catch a round and chamber it. I have done that hundreds of times. Sometimes it releases by itself, and you got to be quick to get your thumb out of there. If you don't, you might get a case of "Garand thumb"

So a malfunctioning bolt/firing pin would set off the round before it was fully chambered. That's got to be what happened.

Well, no...that is not the normal way to release the bolt. Stuffing a full clip into the clip well activates a series of parts that release the bolt and chambers a round. If you have to slap the op rod, there is something "not right" in the succession of 8 (or more) parts. I own and shoot 35 of these Garands. I don't have to slap the op rod on any of them to chamber a round.

But that is "off topic" wrt to your dilemma, so......

The question is why did it fire when you did slap the rod. Still not sure what the circumstances are that would cause this.

Also, not to insult your knowledge of Garands, but you mentioned that you have ordered a new bolt. You are aware that a bolt has to be fit checked to your gun with a set of head space gauges-right? Too little or too much head space will cause other unpleasant "events". Not all bolts are the same......and sometimes you have to try two, three, or more bolts to get the "Goldi Locks" fit.

[Sir Toast]

No need to. Straighten a paper clip, bend one end 1/4" up 90 degrees and file to a point. Run it inside the case, and rake it up on the inside wall. If incipient separation is imminent, the point will snag in the internal groove.

I check ALL my fired centerfire rifle brass this way, before processing.

https://aussiehunter.org/cartridge-case-head-separation/

Thanks for the tip Bossman. Seriously, I never knew this. I'm going to start doing this.

[sofbak]

Thanks for the tip Bossman. Seriously, I never knew this. I'm going to start doing this.

Pro tip: File that point on the end of the paper clip before you bend it.

[pacrat]

OP said:

As far as how many times I have reloaded the brass -- about 3 or 4 times.

OP, have you checked the "headspace" on your rifle? If you happen to have a "long" chamber, even 3 or 4 loadings will overwork the cases to point of failure.