restore PEM

[BountyHunter]

I have a pristine round receiver 91/30 ex sniper with the filled in holes for a side mount. The bolt is being turned down now.

I found a Ukranian copy PEM scope that is 1.75-1.78 in diameter. it came with the topmount base and rings for a round receiver.

The only side mount available is the accumounts which is 27mm or 1.6 inches in diameter at $250.

I am not sure the scope can fit in the accumounts rings due to the size difference. I do not want to spend the money for the mount, drill out the holes and then find out they will not work together.

Anyone have any experience with this mount and the Ukranian scope? Will they work or should I just have new holes drilled and tapped and go to the top mount.

thanks

Information

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[AGB-1]

Make or buy some shims for the scope. AGB-1

New Scope Ring Adapters Reducers Spacers Shims Wide 30mm to 1” | eBay

[BountyHunter]

Make or buy some shims for the scope. AGB-1

New Scope Ring Adapters Reducers Spacers Shims Wide 30mm to 1” | eBay

Scope is bigger than the rings. Sure do not need shims

[AGB-1]

My mistake: I over read your post and had shimming on my mind. I would post this problem over at gunboards.com
because there are lot of knowledgeable people (on mosins) over there.Try a post in the collectors section of that board.AGB-1

[Bruce_in_Oz]

If you want ti fit that scope, AND there is sufficient "meat" in the rings, it is not a colossal task, just fiddly.

If you want to do it yourself:

The big trick is to bore out the rings;

ROUND,
Concentric,
Neatly.

I would think that the following might work:

MEASURE it again!! (old workshop axiom: Measure TWICE, Cut ONCE!!

What you need is a a parallel bar of the same nominal diameter as the existing rings and of about 300mm length.
Precisely centre-drill each end of a steel bar of slightly larger diameter than the ring size.
Turn to the required diameter between centres. Check your parallelism FIRST.
Clamp the ring assembly onto the centre of this bar.

Now comes the "fun bit.
You need to use "goodies" from you box of "packing / accessories" to clamp the base of the mount to the cross-slide. Some creativity involving the tool-post may be involved.
With the centering bar still in place, clamp the base of the mount to the tool-post or other fixture, ensuring there is no nasty "loading" on the bar.

Once you are happy with that setup, take note of the "gap" in the rings where the screws clamp them up; before machining you will need to shim this gap and then tighten the lock screws. If you just wind the lock screws up tight without shims, you will end up with an eccentric hole that is a loose fit on the new scope.

To open out the rings, you can either use a nice, adjustable reamer ,a large boring bar running between centres, or just find an appropriate diameter twist drill; we are not building F1 engines here. A SLIGHTLY "agricultural" surface grade on the inside of the rings will help grip the scope against recoil.
The rest is a simple "measure TWICE and cut once" sequence until a diameter a few thou under scope diameter is achieved.

Alternately, trot down to your local gunsmith (who SHOULD have all of the gizmos mentioned above) and explain your requirements: he probably needs the business. Then check your bank balance.

[vintage hunter]

Unless you have the necessary skills and tooling I suggest taking it to a machine shop to start with, they do this sort of thing every day. Plus it's a heck of a lot easier to find a good machine shop than it is a good gunsmith who's up to the task. At least it is around here anyway.

[Claven2]

In my shop, I would drill and tap a fixture block and mount the rings/base onto it, then attach to the cross-slide of the lathe. You have to make sure to lock the gib for the cross-slide or the backlash in the cross-slide screw will bounce the rings around during machining. You DO need to shim between the top and bottom of the rings!! Then I'd use a boring bar to rough out the cut slightly undersized. Finally, I'd lap it to final dimension with a lapping bar of the same diameter as the scope and valve grinding compound in a vise.

But there is more than one way to skiing a cat. This is NOT a 5 minute job. Expect it to be expensive to have a machinist do this for you, though it MIGHT be cheaper if the shop has enough progressive reamer sizes to just do a quick hand-ream job in the vise. That's doubtful though.