1943 Tula Mosin Nagant 91/30 PU

I recently picked up a Mosin from SOG. All stamped matching numbers except the scope. It's an original scope, just not the one that was originally armored for the rifle.
Here is my dilema: The mount base is the original for the rifle, but the mount is not and the reticle is off to the left so I know I will have to shim, but I would prefer to shim between the rear base and receiver than between the mount and base. I can remove the base locking screws, but the other two are stuck and will not budge. Has anyone else had that problem or a suggestion on how to get the screws out?
Thanks in advance.

Get a good penetrating oil first and let that work on the screw threads to try an loosen it up.

As I understand it the mount is the part screwed to the receiver and the base is the part that cradles the scope. The correct place to shim is between base and mount, not mount and receiver. Go to Mosin Nagant and click on ''sniper section'' and read the article on sighting in PU snipers.
It's been my experience that a shim.001'' thick will shift POI approx. 1'' @ 100yds.

Vintage Hunter,
The mount base is the part attached to the receiver and the reason I would prefer to shim there is so the shim won't drop out if I remove the scope mount.

Well it's yours to do with as you please but anything worth doing is worth doing right. Anything else falls under the category of Bubbarizing, AFAIC.

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Originally Posted by gunsmith63

The mount base is the part attached to the receiver and the reason I would prefer to shim there is so the shim won't drop out if I remove the scope mount.

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Not a good argument. The shim can be fixed to the outside surface of the base with a dab of Pattex/Thixofix or whatever your local version of the rubbery impact adhesive is called. And recoil shock will NOT break the bond - I have (for test purposes) several times attached foresight ring inserts to rifles with a blade foresight, so I could make a better test of the rifle instead of my eyesight - in fact, I even have a backsight attached to a rifle with this stuff! And if you ever need to remove the part, the rubbery glue can be peeled off without damaging any blued or parkerized surface.

And in this way, you can avoid FUBARING an original rifle, as vintage hunter has already tactfully pointed out.

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Originally Posted by gunsmith63

but the mount is not and the reticle is off to the left so I know I will have to shim,

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If you mean that the blade is over to the left within the field of view when the scope has been adjusted to hit center, then referring to the article already linked in a previous post will show you that, in fact, you need to grind, not shim! Which makes the whole discussion with regard to the base and shimming somewhat superfluous.

Ok folks,let me be more precise. I don't want to cover the two base screws with a shim as I feel that would look like a bubba. Neither do I want to put a noticeable shim on the back of the mount as that would also be a bubba. Concealing the shim between the base and receiver seems to be the best as it would always be hidden and no one would see it, but the danged screws are not coming loose.

Patrick, The blade point is centered in the field of view. Elevation is set to 1 and windage to zero, so I need to move the scope objective to the right. I used a collimator to adjust the elevation screws for 100 yards but in the collimator grid the the verticle reticle is far to the left. I don't want to just turn the turret to bring the windage over. I can also see the ghost image of the front sight pin and hood are to the lower right of the scope sight picture. I hope I'm making sense here. The Mosin is in almost pristine condition and all the numbers match so while it has been refurbished, none of the original parts have been replaced. This is my first Mosin but not my last.

Who gives a big red rats arse if the shim is visible as long as it's in the right place. Have you never seen an original 1903a4 sniper? The base or mount or whatever it's called was machined so as to make even contact with the receiver sidewall. Placing a shim in the wrong spot and retightening the fasteners can sometimes cause troubles. Also the screws probably won't index correctly for the set screws to be replaced. The size of the shim needed to do it right is about 3/8''x 1/2''x whatever thickness is required. Only thing it will cover up is the rear dowel pin. Go down to your local hardware or auto parts store and buy a cheap set of feeler gages, the width is right so all you need to do is determine the thickness, cut off a 3/8'' long piece and bobs your uncle.
Just noticed this is a Tula sniper, seems I read somewhere they are a bit scarcer the Izhevsk's.

Gunsmith63, forget the shimming idea for a minute, I just remembered another way to do it. On the backside of the mount there are two ribs at the rear that make contact with the base, if you were to file the top rib that would cause the scope and mount to roll to the right as the thumb screw is tightened. No shims to loose or fiddling with a nice collectors piece required. :cheers:

Have you shot the rifle, yet? I would invest in an inexpensive laser bore sighter, rough it in, and then take it out to the range to assess the POA vs POI. It may just be that the turret has moved. These rifles, assuming you have one of the refurbs and not a repro, should have already been rough sighted. Can you post pictures of the scope and mount?

I have 4 PU snipers - a CAI repro, an original '43 Tula, a restored '42 Izhevsk ex-sniper and a '43 Tula restored ex-sniper. The only one that required a shim was the repro.

These are my PUs. I have a nice unground original mount and a '43 Progress scope that are just itching to get remounted on an ex-sniper, too. :lol:

Attachment 43153

if it's off to the left then you have to trim not shim ,you shim when it's off to the right

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Originally Posted by SVT-40

if it's off to the left then you have to trim not shim ,you shim when it's off to the right

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It all depends where you are shimming/grinding. You are right if working on the front of the mount - making adjustments at the rear would be the opposite.