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  #81  
Old 12-07-2014, 02:54 AM
lapriester lapriester is offline
 
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Location: Cobb, N California
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Originally Posted by Ohio Don View Post
Nice writeup Larry.

I ran into something recently that had me thinking. I remove a barrel with only minor troubles. The problem came in when the replacement barrel was tried. Better than 15 before alignment the combo was tight. About a half hour of work with valve grinding compound and a batch of times in and out finally got it to lock solid at the right spot.

What did you use the valve grinding compound on? Just curious.

Sometimes they are tight, especially Criterions but, I've never had one not index by working it tight and loose several times until the barrel indexed. Maybe I've been lucky. One thing that can be done it it's impossible to index in that way is to take the barrel to a good machinist and have them put it on a lathe and take just a touch off the very inside edge of the barrel shoulder. Not setting back the entire shoulder but just a very slight touch at the very inside with the tool. That very slightly narrows the metal that has to be crushed and makes it easier to achieve index.

When I attended school they did that with every new Garand barrel before installation before even trying it on the receiver to see how close it was to begin with. I tried the Criterion I brought before they cut it and it was close so I wouldn't let them machine it. And, like I said, since then I haven't had to do it even with as much as a 15 degree shortfall.
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  #82  
Old 12-07-2014, 10:31 AM
Ohio Don Ohio Don is offline
 
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Location: S Florida and SE Ohio
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Originally Posted by lapriester View Post
What did you use the valve grinding compound on? Just curious.

Sometimes they are tight, especially Criterions but, I've never had one not index by working it tight and loose several times until the barrel indexed. Maybe I've been lucky. One thing that can be done it it's impossible to index in that way is to take the barrel to a good machinist and have them put it on a lathe and take just a touch off the very inside edge of the barrel shoulder. Not setting back the entire shoulder but just a very slight touch at the very inside with the tool. That very slightly narrows the metal that has to be crushed and makes it easier to achieve index.

When I attended school they did that with every new Garand barrel before installation before even trying it on the receiver to see how close it was to begin with. I tried the Criterion I brought before they cut it and it was close so I wouldn't let them machine it. And, like I said, since then I haven't had to do it even with as much as a 15 degree shortfall.
The barrel shoulder that goes against the receiver. Didn't do anything on the receiver side other than like you'd see on a valve job. I wanted to try that before trying a lathe cut. As it turned out, no need to put it in the lathe. Strange part of it all is that it was a used 1953 barrel.
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  #83  
Old 12-08-2014, 01:16 AM
lapriester lapriester is offline
 
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Originally Posted by Ohio Don View Post
The barrel shoulder that goes against the receiver. Didn't do anything on the receiver side other than like you'd see on a valve job. I wanted to try that before trying a lathe cut. As it turned out, no need to put it in the lathe. Strange part of it all is that it was a used 1953 barrel.
"Strange part of it all is that it was a used 1953 barrel"

And a nice tight one

I've also seen someone take a very fine precision diamond stone on a Dremel and grind that narrow groove on the barrel side edge of the shoulder all the way around. A painstaking process but it works if you don't have access to a machinist or don't know one that you can trust not to muck up the tiny touch with the tool.
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  #84  
Old 12-08-2014, 08:07 AM
Ohio Don Ohio Don is offline
 
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Originally Posted by lapriester View Post
"Strange part of it all is that it was a used 1953 barrel"

And a nice tight one

I've also seen someone take a very fine precision diamond stone on a Dremel and grind that narrow groove on the barrel side edge of the shoulder all the way around. A painstaking process but it works if you don't have access to a machinist or don't know one that you can trust not to muck up the tiny touch with the tool.
I have a Dremel Tool but would use the lathe before using it. A nice sharp carbide tool in the lathe is far more accurate than the hand held Dremel.

My guess is that in your class the reason for the lathe cut was the fillet radius was too big on the barrel. So either a cut on the barrel or a bevel on the receiver was needed. Better to always cut the throwaway part.

A tight barrel to receiver fit is a good thing. I'm wondering if that is why the CMP didn't use this barrel. Bore, headspace, and finish all are acceptable. And it takes a little effort to push the gas cylinder on or off.
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  #85  
Old 12-18-2014, 01:18 PM
Unclenick Unclenick is offline
 
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I think maybe it was in Kuhnhausen that I first saw the advice to, when turning a shoulder forward, go in at a 1 angle off-square so you cut angling slightly toward the muzzle closer at the inside radius. That leaves you the option to stop before actually taking anything off the very outside edge of the shoulder. It's another variant on making the inner shoulder recess Larry described, albeit shallower.
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  #86  
Old 12-18-2014, 11:25 PM
Ohio Don Ohio Don is offline
 
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Originally Posted by Unclenick View Post
I think maybe it was in Kuhnhausen that I first saw the advice to, when turning a shoulder forward, go in at a 1 angle off-square so you cut angling slightly toward the muzzle closer at the inside radius. That leaves you the option to stop before actually taking anything off the very outside edge of the shoulder. It's another variant on making the inner shoulder recess Larry described, albeit shallower.
In his 2003 Ruger pistol book he recommended cutting a bevel in the frame to clear the fillet. 90 cut on the barrel. In his 1986 S&W pistol book, he said to diamond hone the barrel shoulder in a lathe.
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