Help with Broken Bolt Damaged Receiver M1 Carbine

[manteo97]

A most unfortunate failure, but is all to common with bolts. Cause of bolt failures are usually over pressure or excessive headspace or metal fatigue. The method of failure is the right lug cracking, then breaking off, with crack starting on the back of the right hand lug in that tight radius where it meet the bolt body. I've never come across a USGI bolt that was either below or above hardness spec.

What maker's marks were on the bolt, ie who made it?

Did you get this carbine's headspaced checked before you shot it? You can still headspace it with the broken bolt, be sure to strip it first, and see if this was the problem.

Glad to hear you are getting gunsmith(s) to look at it, but make sure they know M1 carbines.

If you have a micrometer, or vernier, check the outside width of the receiver in two locations, one right adjacent to that nicked spot, and the other more rearward, close to the web in front of the dovetail. What you are looking for is to check and see if the receiver has bulged out. If it has, your receiver is done. If it seems that it has not bulged out during failure of the bolt, you are probably going to be able to save this receiver.

Here's why: The recoil load on the bolt during the firing cycle is handled by the right hand lug, the smaller left hand lug is a guide for the bolt right after rotation, during recoil, so once rotated the left lug relief cut in the receiver aligns the bolt during its travel backward & forward.

If that nick is dressed out, the left lug of a replacement bolt will do the job. Do not have anyone attempt to repair weld that area, as it will degrade the strength in this region, put there by the original heat treating.

If and when you decide to get a replacement bolt, and you are not trying to retro-match it (ie flat Rock-Ola), get a USGI round bolt, and ensure that it's not a commercial one.

[a1parrothead]

Thank you for all the information. I will be careful who repairs it, and will check my barrel.

Jeff

[INLAND44]

I'd say that was a hot round. I can't help you on the receiver question but would think that if it can be built up and worked back into shape, you will at that time have to re-Parkerize at least the receiver. Don't take what you think is the easier way and try to do the barreled receiver because you will have to remove the gas piston. Sometimes you will cross-thread the piston nut on reassembly and crack the thin gas block at which point your carbine is toast. And removing the barrel is no fun either because it requires specialized equipment to avoid twisting/breaking the receiver. And make sure you check that receiver for deformation like Manteo said before spending a nickel on repairs. I'm sorry to say I think you are in serious trouble with that carbine.

[a1parrothead]

Thanks for the advice!
Jeff

[DaveHH]

I remember a few years back some guy had a couple of bolts break and BQ explained to us all that that the bad left slot was the cause. As a matter of fact he said that you could keep on putting new bolts in and they would keep on breaking. That receiver has only one shot at being salvagable and that would be to weld up a fix and have a good machinist try and save it. People forget that some of these carbines were run as M2s and God knows how much that beats them up. The owner has got to understand that the carbine needs a couple of things to work well, cases that are trimmed correctly and a bolt that closes correctly with a good fit on both sides. I would suspect that that receiver was already messed up and when the bolt let go it was REALLY messed up. Because the left slot is just a guide the repair might survive well in spite of not being reheat treated.
Take a look an an AK47 bolt and slot sometime. The left hand lug will not even be touching the wall of the slot while the right side will be fit perfectly. With the carbine, if there is anything that limits the touching surface of that right lug, it really puts a strain on an already fragile bolt. A banged up left lug that sits slightly crooked in its slot will doom the right lug unless you have an exceptional one and I don't think that there are that many perfect ones.

[a1parrothead]

Great information. If I can have it safely repaired, I will.

Jeff

[firstflabn]

Did you get this carbine's headspaced checked before you shot it? You can still headspace it with the broken bolt...

Such a measurement would be invalid. Once past its elastic limit, a material cannot be brought back to the same position as prior to applying the load. To fracture, a specimen has been loaded way beyond its elastic limit. Basic material science.

[painter777]

Jeff,
Fortune Telling Bruce has this extra Bolt he said he'd give you a deal on, and wanted me to mention it. He said the Pitting was from the volcanic ash on Iwo Jima !!!

[CINDERS]

Bit of fine filing work like Brian Dick has mentioned doing No.32 scope tubes, some fine emery paper then autosol and that bolt will be as good as new Painter but just a tad undersized

[a1parrothead]

Painter777,

That looks like the correct bolt for my carbine. Do you think Fortune Telling Bruce would take $250.00 for it? With the expense of the receiver, that's about all I could offer him.........

Jeff