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Discussion Starter · #1 ·
I don't know where they can be purchased. Maybe one of our members will step up an offer to do a little machine work.

If you decide to install Brass Shims remember they compress, so, you will need to use a Brass shim that hand sets the lock at 5;00 o'clock instead of 5:30.

I have never like the idea of using more than one shim, SS or Brass. The method I use is simple and quick and almost fool proof, almost... With the rod and spring assembled and a clean gas system unscrew the plug until the forward movement of the rod is complete. Screw the plug back in until it lightly touches the end of the rod. Using a feeler gauge determine the gap between under lip of the plug and the top of the cyl... Lets assume that measurement is .020". Have a brass shim made to .003" to .005" thicker, .023" to .025"... This is how I machine mine, working to this small measurement I usually make a half doz. or so before I get the measurement hoped for.. Nothing wrong with having a few extra on hand, they may work for the next build. Sound likes a PITA , well it is just that, but it is worth it. Art
 

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Va Bene
Sorry All I cant Help it, Grand Ma came from the Old Country
 

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I don't know where they can be purchased. Maybe one of our members will step up an offer to do a little machine work.

If you decide to install Brass Shims remember they compress, so, you will need to use a Brass shim that hand sets the lock at 5;00 o'clock instead of 5:30.

I have never like the idea of using more than one shim, SS or Brass. The method I use is simple and quick and almost fool proof, almost... With the rod and spring assembled and a clean gas system unscrew the plug until the forward movement of the rod is complete. Screw the plug back in until it lightly touches the end of the rod. Using a feeler gauge determine the gap between under lip of the plug and the top of the cyl... Lets assume that measurement is .020". Have a brass shim made to .003" to .005" thicker, .023" to .025"... This is how I machine mine, working to this small measurement I usually make a half doz. or so before I get the measurement hoped for.. Nothing wrong with having a few extra on hand, they may work for the next build. Sound likes a PITA , well it is just that, but it is worth it. Art
Thanks Art.

Maybe I will set up production . . . Gonna check into it.
 

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I get my brass shim stock from a local hobby shop that deals in radio control planes, cars, etc.
They have a good selection of brass & aluminum, and also wire gauge steel rods.

Another alternative for aluminum is from cans, or rain flashing from home supply store.

Jay Kosta
Endwell NY USA
 

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Discussion Starter · #6 ·
Good idea

I get my brass shim stock from a local hobby shop that deals in radio control planes, cars, etc.
They have a good selection of brass & aluminum, and also wire gauge steel rods.

Another alternative for aluminum is from cans, or rain flashing from home supply store.

Jay Kosta
Endwell NY USA
Thanks Jay, A punch set is the way to go, I turn mine on the lathe and part them off, lots of waste material, trying to find Brass round stock in Kerrville Texas is out of the possibility of Mankind. art
 

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Shim

Art, are you shimming the gas plug or the gas cylinder? Is the purpose to increase dwell time or something else?
Steve
 

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Art, are you shimming the gas plug or the gas cylinder? Is the purpose to increase dwell time or something else?
Steve
I have a die to punch out shims. The ones i have been making and selling here on the forum have been made from S.S. When i get back to work later this week i will see about making some from Brass. The only problem with the soft brass is that when you start getting down to thinner material like the .003 and .005 thickness the brass wants to flow around the punch and not shear cleanly like the harder S.S. So i will have to tighten up the clearence on the punch and die in order to get a burr free shim. The biggest problem with less punch and die clearence is that there is a greater chance of shearing the punch which will give you a large burr on the shim. Its difficult to use one die to punch different thickness material because of maintaining the proper percentage of die clearence in order to produce a burr free part.
 

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Discussion Starter · #9 ·
Two responses..

The purpose of using shims is to tighten the gas system up on the barrel in a drive back manner. The shims go behind the front band up against the shoulder on the barrel

Thin shims, anything under .010", I try to avoid if possible, both SS and Brass will crack from the heat and cooling plus recoil. I have seen them fall out a few times. BrassShims are not for everybody, some people like the idea of SS being stronger. Brass shims have served me well over the years, so it is natural to stay with them.. Never tried to use a die punch set to make them from sheet material. Turing brass round stock down is not time effective if one is thinking about selling them.
For the M1A owner that has everything of top quality, and we have a number of such owners, it would be worth the trouble to install Brass Shims next time the rifle is down for a full service. This is no a fact, but I feel Brass Shims produce less fouling around the installed area, it appears that way anyhow. Art
 

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Art, the only thing I might have against a brass shim is what type of brass one uses and how quickly it would wear down. Maybe bronze might be something to try?

Anyway, I fully agree that it is better to use a single shim than a combination of shims for longer life of the shims. The only problem is that I lost my source for many shims being made in .001" increments when I retired. I have found that two shims will stand up for quite a long while for civilians though, even NM shooters. That is the reason why one should check the shim fit every year before the beginning of the shooting season to ensure the shims are still good.
 

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The new SA M1A I have yet to shoot has the operating rod hitting against the plunger (if that is what it is called) when the action is closed. I can unscrew the gas cap a bit and have the OR move forward until it is stopped by contact with the roller on the bolt. Should the roller or the plunger be what stops the forward motion of the OR?

I assume the shims are put under the gas cap to move it and the plunger forward a bit. Do you want to eliminate the contact between the OR and plunger or just reduce it?
 

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The plunger you are refering to is the tail end of the piston, this combined with the gas cylinder plug is what stops the foward travel of the op rod. You must have contact between the op rod and piston. Moving the gas plug and piston foward changes the dwell time of the rifle by increasing the distance the op rod must travel before it unlocks the bolt. The same thing can be done by carefully trimming the tail of the piston. Doing so can sometimes have an effect on the accuracy of the rifle if you know how to do it properly.
 

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Read post #6 from Art again. he explains it there and may I suggest that you read some of the Armourer sections. I think you will find answers to questions you havn't even thought of yet.


The new SA M1A I have yet to shoot has the operating rod hitting against the plunger (if that is what it is called) when the action is closed. I can unscrew the gas cap a bit and have the OR move forward until it is stopped by contact with the roller on the bolt. Should the roller or the plunger be what stops the forward motion of the OR?

I assume the shims are put under the gas cap to move it and the plunger forward a bit. Do you want to eliminate the contact between the OR and plunger or just reduce it?
 

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Read post #6 from Art again. he explains it there and may I suggest that you read some of the Armourer sections. I think you will find answers to questions you havn't even thought of yet.
+1. It's all there, take your time. If your op rod isn't closing all the way forward against the bolt roller you won't hurt anything to stick a thin shim in there, but mic it off the gas plug first so you'll be right with the shim's thickness. That should improve the dwell. The port in the gas cylinder is large enough relative to the gas port in the barrel that you still should have ample gas.
 
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