NR M1 carbine gas system brazing

[D-BOMB]

Hey all,

I recently picked up a USGI M1 carbine that has had a Non Restricted length barrel fitted. Where the gas system meets the barrel, the brazing seems to have some flaking or cracking. The seller had put a couple hundred rounds through it with no issues and he sent photos to a M1 carbine guru that says it may just not have been cleaned up on the lathe as well as it could have been when the barrel was installed. But if he had put that many rounds through it with no cycling issues it should be fine.

I understand it is not a factory job with these USGI rebarrels and they wont be perfect, but is this anything to worry about? If it becomes an issue would it be as simple to just have it rebrazed?

[/url]DSC_0465 by D-BOMB50, on Flickr[/IMG]

[/url]DSC_0462 by D-BOMB50, on Flickr[/IMG]

[/url]DSC_0461 by
D-BOMB50, on Flickr[/IMG]

[/url]DSC_0459 by D-BOMB50, on Flickr[/IMG]

Thanks all

 

[fingers284]

Well it ain't purty is it. What I would do with it if it were mine is wrap some very white paper around the joint and use a cleaning patch to swab a little oil in the barrel (the pressure vent will catch a small amount as the patch passes by), then fire it, if there is any blow bye leakage, it will show up as a discoloration on the paper. If any leakage is evident it will be up to you to decide if you consider it "excessive" and have it re-done or if it is a minimal amount and just carry on. If it is minimal you can periodically re-do the test to see if the problem is getting worse.

 

[D-BOMB]

Well it ain't purty is it. What I would do with it if it were mine is wrap some very white paper around the joint and use a cleaning patch to swab a little oil in the barrel (the pressure vent will catch a small amount as the patch passes by), then fire it, if there is any blow bye leakage, it will show up as a discoloration on the paper. If any leakage is evident it will be up to you to decide if you consider it "excessive" and have it re-done or if it is a minimal amount and just carry on. If it is minimal you can periodically re-do the test to see if the problem is getting worse.

That is a good idea thank you! So in the event that it does get excessive would it be as simple as to have a gunsmith redo the brazing?

 

[bearhunter]

It's impossible to tell from your photos very much about the method used to fit the gas and guide rod system to the barrel.

Was it done as a barrel insert into the gas section as it used to be done commercially many years ago by companies like Plainfield and a few others or was each section manufactured and individually brazed to the barrel?

Brazing can be very good if it's done properly but in the case of sleeving a barrel the tolerances would have be large enough to allow the flow of the metal between the pieces. Then, the gas port would need to be cleared of brazing metal as well and hopefully it didn't get into the bore.

I have sleeved barrels for my own use and use Titanim Putty. It is very strong but a lot easier to use and doesn't require so much heat. I usually use the gas port block and the guide block all the way back through the threaded section to do my jobs. Thousands of rounds down one with a Shilen take off match barrel that is 26 in long without an issue and a very accurate Carbine it is.

The problem with brazing is that if it isn't done properly at the proper temperatures the bonding metal won't flow properly over every thing it needs to. Even then, it is definitely a chore for experts.

One way to tell if the brazing metal has penetrated far enough is to check inside the gas block by taking out the piston and nut. You should be able to shine a light in there and see brazing material. You should also be able to see it at the chamber end, depending on how it was done.

Machining the whole gas system and guide rod track is a tricky maneuver. That's why many of the companies that cloned the M1 Carbines in the fifties and sixties used the back half of scrapped milsurp barrels as sleeves. Even the barrels Tradex offered had those components separately machined and added as sleeves. They weren't bad barrels either. I wish they would bring more in. From what I could see, the components had been tinned then heated up evenly, slipped together and a bit of extra solder added to make sure everything was filled properly.

You can get away with quite a bit on these barrels because the pressures are so low. IMHO, if you remove the gas block nut and the piston to look inside for traces of brazing compound and find it, all should be well. Keep an eye on the operating rod guide to make sure it isn't binding. I suspect if your whole system is sleeved in separate units that will be the first part to give you and issues. Also, it should be where you will start to notice any escaping gasses. Check the seam on the gas port block where they fit together. If it's going to happen at all, that will be where it will occur.

 

[D-BOMB]

It's impossible to tell from your photos very much about the method used to fit the gas and guide rod system to the barrel.

Was it done as a barrel insert into the gas section as it used to be done commercially many years ago by companies like Plainfield and a few others or was each section manufactured and individually brazed to the barrel?

Brazing can be very good if it's done properly but in the case of sleeving a barrel the tolerances would have be large enough to allow the flow of the metal between the pieces. Then, the gas port would need to be cleared of brazing metal as well and hopefully it didn't get into the bore.

I have sleeved barrels for my own use and use Titanim Putty. It is very strong but a lot easier to use and doesn't require so much heat. I usually use the gas port block and the guide block all the way back through the threaded section to do my jobs. Thousands of rounds down one with a Shilen take off match barrel that is 26 in long without an issue and a very accurate Carbine it is.

The problem with brazing is that if it isn't done properly at the proper temperatures the bonding metal won't flow properly over every thing it needs to. Even then, it is definitely a chore for experts.

One way to tell if the brazing metal has penetrated far enough is to check inside the gas block by taking out the piston and nut. You should be able to shine a light in there and see brazing material. You should also be able to see it at the chamber end, depending on how it was done.

Machining the whole gas system and guide rod track is a tricky maneuver. That's why many of the companies that cloned the M1 Carbines in the fifties and sixties used the back half of scrapped milsurp barrels as sleeves. Even the barrels Tradex offered had those components separately machined and added as sleeves. They weren't bad barrels either. I wish they would bring more in. From what I could see, the components had been tinned then heated up evenly, slipped together and a bit of extra solder added to make sure everything was filled properly.

You can get away with quite a bit on these barrels because the pressures are so low. IMHO, if you remove the gas block nut and the piston to look inside for traces of brazing compound and find it, all should be well. Keep an eye on the operating rod guide to make sure it isn't binding. I suspect if your whole system is sleeved in separate units that will be the first part to give you and issues. Also, it should be where you will start to notice any escaping gasses. Check the seam on the gas port block where they fit together. If it's going to happen at all, that will be where it will occur.

Thank you for the detailed reply, I do believe it is sleeved into the gas system. I was not to knowledgeable on the anatomy of the M1 Carbine's when I first got it, so it photos I thought the brazing was done where the receiver meets the barrel,I now know that is incorrect.

I was more concerned with this as a safety issue but it seems that if it failed it would more than likely just fail to cycle from venting to much gas(?).
If worst case scenario would it be possible to just rebarrel the with a new one if it ever needed it and a repair wasn't viable? I am really wanting to keep this USGI receiver.

 

[sunray]

If it worked ok for a couple hundred rounds, it's very likely as safe as it'll ever get. Any indication of who made the barrel?

 

[D-BOMB]

Thats what I was thinking, the photos make it look worse than it does in person so I am thinking it is just not finished as well as it could be.
Not really sure who made the barrel.

 

[bearhunter]

Thats what I was thinking, the photos make it look worse than it does in person so I am thinking it is just not finished as well as it could be.
Not really sure who made the barrel.

On this very rare occasion sunray is likely correct. You need to be very careful following any of his advice.

The biggest problem you will encounter will be finding a replacement barrel.

I am surprised Tradex or SFRC isn't bringing some in at reasonable prices. Some shops will build new ones for you. Bits of Pieces will do it but extremely expensive as they have a lot of machining to do as well as set up to get them right. One offs are very expensive to have done.

 

[Manteo97]

The brazing in the photos appear to be cracked where the barrel fits into the gas block/barrel stub. If that's the case, then the brazing has been done incorrectly. What may be happening is that the barrel sleeve is separating from the gas block/barrel stub due to firing. 100 rounds is not enough to see what really going to happen when more rounds are fired. If you can see the breech end, see if there is any brazing here that has been machined down. It should have been brazed at both ends.

More important is a head space check. If you have access to gauges, it should be done, before you re-braze it. The movement of the barrel sleeve will increase the headspace, it may be out of spec. If that's the case, it is unsafe to shoot.

Bearhunter is correct when he referenced post WW II commercial carbine makers, they used this technique, mostly using surplus M1903 30-06 barrels machined down. Two methods were used, one was sweat soldered, the other was cutting a 1/2-32 thread on a portion of the sleeve, and threading the bored out gas block/barrel sleeve, and then sweat soldering. The trick with this technique is to ensure the axis of the bore of the gas block/barrel sleeve is concentric with the bore of the barrel. No one brazed, as sweat soldering was cheaper & faster for production. Both National Ordnance and Universal did this.

 

[D-BOMB]

The brazing in the photos appear to be cracked where the barrel fits into the gas block/barrel stub. If that's the case, then the brazing has been done incorrectly. What may be happening is that the barrel sleeve is separating from the gas block/barrel stub due to firing. 100 rounds is not enough to see what really going to happen when more rounds are fired. If you can see the breech end, see if there is any brazing here that has been machined down. It should have been brazed at both ends.

More important is a head space check. If you have access to gauges, it should be done, before you re-braze it. The movement of the barrel sleeve will increase the headspace, it may be out of spec. If that's the case, it is unsafe to shoot.

Bearhunter is correct when he referenced post WW II commercial carbine makers, they used this technique, mostly using surplus M1903 30-06 barrels machined down. Two methods were used, one was sweat soldered, the other was cutting a 1/2-32 thread on a portion of the sleeve, and threading the bored out gas block/barrel sleeve, and then sweat soldering. The trick with this technique is to ensure the axis of the bore of the gas block/barrel sleeve is concentric with the bore of the barrel. No one brazed, as sweat soldering was cheaper & faster for production. Both National Ordnance and Universal did this.

Thanks for the reply, judging by your sig line do you do work on M1 carbines?

 

[Manteo97]

Yes, I work on M1 carbines. Thanks, got your PM, we'll talk,