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Left Receiver lug wear.
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TWC497 View Drop Down
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Joined: Jan 25 2023
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    Posted: Jan 26 2023 at 8:23pm
Hello, I'm new to the forum.
 I have been looking around on the topic of M1 carbine bolts breaking and causing wear or burrs on the left locking lug of the receiver. 
I have a Plainfield M1 carbine and when cleaning the other night, I noticed the left lug was worn. I have had the gun about five years and fire it regularly it's never had a problem and I'm not sure the damage was there when I bought it or not. I'm wondering if this gun is safe to fire and if the worn lug could be tig welded up? I'm thinning the first step would be to buy headspace gauges and check the gun in its current state.  
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Points: 214 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Jond41403 Quote  Post ReplyReply Direct Link To This Post Posted: Jan 27 2023 at 4:03pm
Yes, definitely buy you some gauges to check the headspace just to be safe. All you would really need is the no-go and the field gauge. You don't need the go gauge. as far as fixing the lug, the experts will be a long shortly to help you with that if it can even be done.hth
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I’m thinking it left the factory that way. That Plainfield left lug is not machined exactly like a USGI on the underside. As long as the left lug smoothly drops and retracts in it’s channel, probably ok. You’ve been shooting it a good bit and if head space was tight, you’d probably know it by now.
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Maybe I am missing something, but that left lug does not look excessively worn to me. 
Wayne
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Originally posted by W5USMC W5USMC wrote:

Maybe I am missing something, but that left lug does not look excessively worn to me. 

Me either. I think OP is looking at the underside which is not machined exactly like a GI.
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That's what threw me off is the difference in the lugs from a plainfield to a USGI, but then again I didn't know there was a difference between the two. I just know it doesn't look like my lug haha. If he intends to shoot his carbine often it would still be wise to buy those gauges just for peace of mind. I have a c39 V2 that the head space is walking off and I check with my gauge before every range trip just to get as much use out of it as I can before it becomes too dangerous. It's problem is chipping of the right locking lug shoulder. I bet he would feel a lot better shooting it after gauging it, especially since he felt concerned to begin with
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Points: 2 		Post Options Post Options   Thanks (0) Thanks(0)   Quote TWC497 Quote  Post ReplyReply Direct Link To This Post Posted: Jan 27 2023 at 8:58pm
I will buy some gauges and keep an eye on it.  Just curious is the left lug there to actually lock the breech or is it there more for a safety in case the right lug on the bolt fails?
Thanks for the replies.
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Points: 89 		Post Options Post Options   Thanks (0) Thanks(0)   Quote bonnie Quote  Post ReplyReply Direct Link To This Post Posted: Jan 27 2023 at 9:28pm
Op, buy all three headspace gauges: go, no-go and field. Don't half-step.
You're concerned with the bolt lugs and receiver lugs. If you do find it necessary to replace the bolt you need to know if it headspaces safely on your carbine.

You might get by with a little excess headspace but you can't with short headspace. Dangerous for the gun and the shooter.
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Wouldn't a go gauge be only useful if you are planning on rebarreling it? I have switched bolts in my carbine without needing a go gauge. The no-go in field told me everything I needed to know.
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Originally posted by Jond41403 Jond41403 wrote:

Wouldn't a go gauge be only useful if you are planning on rebarreling it?

In general, yes and more so when installing a new barrel that may require finish reaming. I like having all three gauges on hand but in reality, the only one I ever use is the field gauge. 
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The left shoulder damage on USGI receivers that I've seen has been what looks like a chunk torn out of the lower part of the shoulder, or a deep impression in the shoulder. I saved some pictures somewhere. Two have been late serial Inlands, though I think that's a coincidence vs a pattern.
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Some of us here use alternative methods to measure head space. I don’t poo-poo owning a full set of gauges, but gauging can be done without them. All you need is a sized case of known length.
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Points: 214 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Jond41403 Quote  Post ReplyReply Direct Link To This Post Posted: Jan 28 2023 at 12:36pm
That's true but I was just trying to save the OP some money from not having to buy all three gauges. Yes you can use resized cases and Scotch tape but I've always liked gauges better. I have never heard of swapping bolts making the headspace dangerously too tight in an already well used carbine and a go gauge in my opinion is not needed in the OPs situation, Even if he did swap bolts.you would only really need The Go gauge if you were going to swap barrels or rebarrel. I own gauges for every caliber of rifle and carbine I own but I have never needed a go gauge. Just use a bullet for your go gauge, when you're checking headspace, it's not like you have a firing pin in your bolt or anything that could set it off anyway to make it dangerous, a bullet is your go gauge. Floyd's suggestion of using resized cases and Scotch tape is the cheapest way to go but the OP would have to be a reloader or have a buddy that reloaded to be able to size the cases for him
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Points: 1930 		Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: Jan 28 2023 at 12:50pm
I agree….the best and cheapest go gauge is the round you’re shooting. Not saying that long brass round is not out there, but from what I have measured, never found one far enough off the mean average from a fresh box to matter. That could always happen even if your head space is a perfect 1.290 and more likely so. I like my shooter actions to be a little lose for that very reason. I watch ammo very closely when shooting my tight carbines.

In some cases, a bolt swap can change head space by a few thousandths, but looking for and finding that bolt that makes a difference is a crap-shoot.Tolerences allow them to vary.
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