Cracked SA M1 Barrel

[AD-4NA]

I noticed my poor M1 has developed a crack in the barrel extending along the "bottom" of the spline for the gas cylinder on my arsenal replacement 12-51 Springfield barrel. I am working on getting another usgi barrel for this mixmaster shooter but I was wondering if anyone else has seen this type of failure?
None of my searches brought up anything relevant instead of receiver failures; I know this is the thinnest part of the barrel but it does seem strange.

Information

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[browningautorifle]

Never even heard of it before. Are you sure it's a crack? Got any close ups of it? We'd like to see this...

[Bill Hollinger]

Yes please. Detailed pictures are a must. TIA

[jmoore]

Would have to SWAG bore obstruction, but photos would surely help! Thinking grease or some such.

[AD-4NA]

Okay, pictures on the way when I get a chance: the mystery continues!
Yes it is most definitely a crack, and it goes all the way through the barrel: it vented gas and powder residue during firing! (that was alarming)
It did not have it when I bought the M1 years ago and I don't think I have had a squib load. All my surplus ammo and a few reloads have gone "bang" and cycled all the way. The barrel is not bulged. Never had grease near the barrel or dropped it in the mud to get plugged up.
I was puzzled since this is a relatively low pressure area, right before the bullet exits the barrel and when the gas is expanded and about to/is exiting through the gas port.

[emmagee1917]

Do you have mud dobbers in your area ? Wasp like critters that lay their eggs in small holes then fill the end with a spit / mud / paper plug .
If you clean a gun and lay it down / prop it in a corner , one of those can plug it in an hour . Had one do it to me , caught it before firing . I now use GI muzzle covers on them the minute I'm through cleaning and leave them on till just before shooting .
Chris

[browningautorifle]

I have a feeling all we're going to see is exactly what he describes and the mystery will continue. It may have just been metal fatigue...which happens. Or a flaw...

[karl schmidt]

weird stuff happens. I had a CMP carbine with a barrel crack. The crack originated under the top of the front the sight and went to the muzzle. I assumed it was some sort of metal fatigue started by the sight key way. you could look in the muzzle and see it inside the barrel. CMP replaced the carbine and paid shipping both ways.

[Calif-Steve]

I went through Infantry Officers Basic Course at Ft. Benning 1969. Fun in July sun deep South. I had the same M14 all the way through the course and it had a terrible habit of throwing off its front sight. I would pick it up and put it in my pocket. At the end of the day I would stick it back on and turn it in. I never thought too much about it until graduation when it had to be really clean or they wouldn't accept it back. Well I took it out into the Georgia sun and discovered the chrome plating under the front sight had chipped off. I could readily see it looking down the bore. Well, I turned it in to the Unit Armourer and stated it needed a new barrel. Well, those words brought the Executive Officer running over to see my rifle. We all walked outside back into the hot sun. We all looked at it and then discovered the barrel was cracked. A long pencil mark, that was all. That was why the chrome was gone. Everyone was amazed I hadn't killed myself, but all was good. They tagged the rifle for a new barrel and I happily departed Ft. Benning.