Ruptured case

Modeler · Jun 15, 2016

So this happened today.

And of course, I wasn't wearing a hat.

It was an FN-49 in 30-06. Ammo was M2 Ball '76 HXP from the CMP. I had loaded 5 rounds in the magazine, and the last round was the one that went off. The neck is still in the rifle, as I don't have a broken case extractor. The barrel itself is (thankfully) clear.

Not sure what caused this. Was it just a bad round? Bad headspace? The casings from the previous 4 rounds were all in good shape, nothing wrong at all. Any thoughts?

v0lcom13sn0w · Jun 15, 2016

i hope you are ok!!!

hard to tell over the internet. could be a lot of things. 40yr old ammo... ive heard in some instances that if ammo gets tumbled or shaken long enough that the powder burn properties can change... headspacing could be the issue too, also an out of battery discharge.

do you have a vernier caliper or micrometer? measure the length of one of the spent cases. that neck looks super long for 30-06. are the primers flattened completely on the spent cases?

Velzey · Jun 15, 2016

First off I'm glad your ok!

From the 100% intact casing, it looks a little fishy to me. Do you have a set of headspace gauges?
I had something very similar happen with an old FN-49 that had been abused. HS was on the high end, and the field gauge wouldn't close, but the no go did.
One round test fired, and it did exactly what we have here.
FN-49's are finicky when it comes to HS.

If you need to borrow a set of gauges just lemme know.

P7M13 · Jun 15, 2016

Dude, that is gnarly! Glad you're OK enough to write this and selfie your powder burns! What do your safety glasses look like?

Arm chair thoughts:

Did it happen when you pulled the trigger?
Do you have the equipment to perform a "not fully locked in battery" fire test? (on a spent round)
It looks like head separation.
Looking at the one spent case, it seems to me it has a lot of burned powder carbon tracks, all the way down the case. Is this typical for shells coming out of your gun? Point being, if your chamber is too sloppy, you will get those tracks. Put an undersized cartridge in there, and with the expansion needed, you increase your chances of rupture. Can you take calipers to a bunch of cases to get a min max spread on the CMP '06 ammo?
If it is powder tracks, recommend taking a cast of your chamber and measuring it.
@v0lcom13sn0w called a good one in asking about head space.

Good Luck!

Modeler · Jun 15, 2016

Well, whatever happened won't happen again. I took the rifle apart tonight (with great difficulty) and it's pretty well bubblegumed. The extractor and it's attendant parts are bent, which isn't that big of a deal; I can replace those. As it was I had to hammer them back into the bolt just to get the bolt to separate from the bolt carrier.

The bolt cover is a little bubblegumed too, but again I can replace that. It's hard to replace a stretched and bent receiver though.

It might not come through on the picture, but the back end of the receiver is bent and stretched/bowed out. And the right-side rail is stretched and deformed inward and downward. The bolt won't hardly slide on it at all.

So my Luxembourg FN-49, one of 6,300 made, is only worth the parts that didn't get damaged.

Sgt Nambu · Jun 15, 2016

That truly sucks, Modeler! But, lm glad your ok!

Velzey · Jun 15, 2016

That right there is an out if battery kaboom! I'm very curious what caused it tho.

PaulB47 · Jun 16, 2016

I once received a pile of miscellaneous 7.62 surplus ammo from a friend of mine who had no need of it. Since I had one of those whiz-bang RCBS Precision Mics, I decided to check the headspace of those rounds. I was astounded to find that about 10% of them were too long for my M1A, according to the fired brass from that rifle. Needless to say, I did not load them up and shoot them. They are marked for bolt gun plinking only.

I don't think it is being too paranoid to check every round that goes into these rifles, particularly the older rounds like this .30-06. Semi-autos are very unforgiving.