Barrel problems with my M1

[MauserMatt]

Long story short, back in the early 2000s my uncle had a squib in his M1 Thompson. He said 5 rounds were stacked in the barrel that he was able to get pushed out. He told me that there was no bulge to the barrel and he didn't see any problems. He passed this Thompson down to me in 2015. I don't know how many thousands of rounds he fired through it since the squib and I've personally put several thousand through it since 2015. I haven't seen keyholing or any other issues. Until now. 

I purchased one of Roger's (Merle's) 22 kits and went to install it. But the 22 barrel is hanging up in the barrel exactly where the squib was. I can see the faintest of lips (I can't get a good picture of it either) that the 22 barrel is hanging up on. I obviously don't want to pound it in there. I've cleaned the barrel real good, but still no luck. Has anyone ever heard of fire lapping a pistol caliber barrel like the Thompson? Should I look for a GI barrel instead of trying to get this one to work? Any other thoughts?

Thank you!

[TD.]

When examining the barrel with a bore light, do you notice a dark circular ring(s) where the squib rounds were stacked in the barrel? M1 barrels, without fins, were so thick it is possible that a visible bulge may not appear on the outside after the squib load incident. However, something definitely happened inside the barrel.  

[MauserMatt]

3 hours ago, TD. said:

When examining the barrel with a bore light, do you notice a dark circular ring(s) where the squib rounds were stacked in the barrel? M1 barrels, without fins, were so thick it is possible that a visible bulge may not appear on the outside after the squib load incident. However, something definitely happened inside the barrel.  

You are correct. There is a very slight ring right where the squib happened. That is the exact spot that the 22 barrel is hanging up.  

[Got Uzi]

Options are pretty simple-replace the barrel and go on with life or you’ll have to machine the outside of the 22lr barrel to fit past the ring. Depending on how far back from the muzzle the ring is, will tell you how easy it would be to machine the liner. If it’s more than 1 or 2 inches back from the muzzle, save yourself the machining nightmare and replace the original barrel. 

[Jeremy]

Agreed...get a green mountain barrel and don't look back.

[reconbob]

  If this is an original military Thompson you should replace the barrel with an original G.I. barrel.

The Green Mountain barrels are AOK, but down the line when you go to sell the gun a GM barrel

is not going to help the cause.

 

Bob

[MauserMatt]

I guess I already knew the answer, but was really hoping it wasn't that. This being a family heirloom, I don't think I'd ever sell. I do want to keep it all USGI though. So looks like I'm on the lookout for a USGI barrel. Wish I had bought one when they were plentiful....

Thank you gents!

[deerslayer]

If you have a very nice matched original barrel on your gun, I think id remove a little material from an inch or so of the outside of the 22 barrel and see if it would slide in another inch.  A few thousandths off the 22 barrel isnt gonna effect anything.

[jim c 351]

If it was my barrel, I  would machine a 2 inch long piece of drill rod to .451 inch, (or what ever the inside dia of the  bore measures) and drive it thru

a well oiled bore with a length or 3/8 inch drill rod.

If machined precisely it should freely slide thru the undanaged part of the parrel, and meet resistance at the bulge.

If you're thinking of scrapping the barrel, you've got nothing to loose.

Jim C

[MauserMatt]

8 hours ago, deerslayer said:

If you have a very nice matched original barrel on your gun, I think id remove a little material from an inch or so of the outside of the 22 barrel and see if it would slide in another inch.  A few thousandths off the 22 barrel isnt gonna effect anything.

Thank you sir. I have access to a lathe at work. This might get me by.... I appreciate the tip! 

[MauserMatt]

1 minute ago, jim c 351 said:

If it was my barrel, I  would machine a 2 inch long piece of drill rod to .451 inch, (or what ever the inside dia of the  bore measures) and drive it thru

a well oiled bore with a length or 3/8 inch drill rod.

If machined precisely it should freely slide thru the undanaged part of the parrel, and meet resistance at the bulge.

If you're thinking of scrapping the barrel, you've got nothing to loose.

Jim C

Very true. Thank you as well!! 

[StrangeRanger]

25 minutes ago, MauserMatt said:

Thank you sir. I have access to a lathe at work. This might get me by.... I appreciate the tip! 

You might want to discuss that concept with the insert barrel maker

 

[MauserMatt]

2 hours ago, StrangeRanger said:

You might want to discuss that concept with the insert barrel maker

 

Also very good point! 

[laurencen]

myself before I did anything slug the barrel and figure how much too small is, if its only a few though as Jim suggests swage it out, if more make a hone and hone the small area to size