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Discussion Starter · #1 · (Edited)
I have a Fin M39 a post war stock with the square dovetail joints. I am the first one to have it apart and there were NO shims in the rifle. I have read a reply that there were some that had no shims because the gunsmith never set them up. Should I add the shims if the rifle needs them? If I do need them what are they made of?
 

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I have a Fin M39 a post war stock with the square dovetail joints. I am the first one to have it apart and there were NO shims in the rifle. I have read a reply that there were some that had no shims because the gunsmith never set them up. Should I add the shims if the rifle needs them? If I do need them what are they made of?
You need a shim only if the barrel does not free float in the stock.

To check, remove the bolt, bands, handguard and action screws.
Support the rifle in a rest. Press down on the tang with your thumb and see if the action rocks a bit. Pressing down on the tang should cause the barrel to rise slightly.

If the first test checks out, replace the magazine housing and screws, but leave the front action screw slack. Observe how high the muzzle of the barrel is above its channel in the stock with the rear action screw tightend fully. Now screw in the front screw and observe the barrel; it should begin to settle back down into the stock channel. When the front action screw is tight, there should be no contact between the the barrel and the wood beneath it. See if you can slide a piece of paper between the barrel and the stock.

If the above checks out, your stock is free floating the barrel. If not, you can place a shim just behind the recoil cross bolt. Use steel, since copper will cause a galvanic reaction and expand more than steel as it gets hot.

HTH
 

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Just to add to this: I have two such M39 in post war stocks.

One had a single shim under tang and two forward under the recoil lug.

One had four under the tang and five forward.

Well...someone did that and its Finn arsenal shims so my conclusion is the post war stocks are
a bit over sized: one size fits all type of thing. That said: I am just noting that several shims
at one or both locations may be needed....if your rife needs any at all. If needs shims,
then its range time and have several of each flavor and try the combinations of them till you achieve
the results Leon mentions and your accuracy is established. THere is a solution to shims...just
got to have patience in finding the combination of them to achieve accuracy. I can say this as
I was lucky, some Finn did that before I bought my two and I was saved this trek. However, it
awakened me to the fact that they used shims in this manner and if I get a rifle without any, I
may be in for some work up till I get the rifle sorted out. You can fabricate shims out of coke cans,
metal flashing, copper thin sheets of metal etc etc. The metal ones will last longer than gasket material
or other softer materials for shims. Its no big deal to make them out of any material and cost is nil.
By all means: if your rifle needs to be shimmed, do not be waved off by the task ahead, it is really easy
as I have done this on every Mosin 91/30 Rifle that I own with awesome results.
 

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If the gun is not shooting straight, you shim it to float the barrel and provide a more stable base for the receiver, if the gun presses against the bottom wood add a shim to the front (0,015" brass), if it presses on the handguard add a shim to the rear of the receiver, also 0.015" brass. if that isn't enough, go up in even increments. when your there, brad the shims in place and have fun!-SDH
 

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Discussion Starter · #7 ·
Could be a DUH moment THIS IS A SHIM, RIGHT ? I was looking by the cross bolt. I read in one of the post they could be under the tang. I thought this was to keep the wood from splitting. And thank you Leon that is a very comprehensive set-up. I should be fairly close, I put it back together the same way it came apart.
 

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Yeah that is a shim and that more than likely tips the action forward and into the barrel chennel farther. Out of about 150 M39's that have passed through my hands Maybe 75 had shims and 75 didn't so don't panic and change the thing all around till you make several range trips and use several different ammo types. The old axiom of if it ain't broke don't fix it is just great when it comes to accuracy at the range. On M39's amd many of the other Mosins I have tightened the action screws to a certain pattern for years. I snug the front most one and then back off one half turn. I then tighten the back one and go back after that to snug the front one. This tends to raise the barrel in the channel if the stock is close to being right and that way float it a bit. I never tighten the band screws on M39's which seems to help also. I push the front band up and tighten the through bolt on it to hold it up and away from the handguard as much as possible too. When the rifle is together and ready to go to the range the barrel muzzle should be able to be moved around in the stock a bit. This helps the barrel harmonics and whip which it will go through. If you find a barrel on a gun with lots of wear on the blue of the barrel from rubbing the wood this looseness was never achived and that is what caused the wear on the blue. I recently bought an M39 from a fellow who said he was very disgusted with the accuracy and wanted to sell it and move on. He had the barrel clamps so tight I had trouble unscrewing them for cleaning. The bore was really nice and off to the range I went after cleaning and setting like I just described. I am not a tack driver of a shooter but this rifle would shoot far better than I could aim it with my old eyes. Somebody over the weekend got a nice rifle and the same info I just wrote and will like what he sees when he shoots it I am sure. You just have to be patient and see what you have first before all your well meaning improvements ruin the whole picture! Bill
 
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