My Son-in-Law has a large ring Chilean mauser in 308 that he wants to maount a scope on. He had a gunsmith drill and tap and mount 2 piece bases. I don't believe he has the proper bases because the Smith tells him he needs a .030 shim under the front base. Can anyone shed some light on this. He bought Weaver bases at Dicks and he say's the package listed the Mauser name. I just don't believe that mounts sold for this rifle should have to be shimmed. Thanks, smoker1

If the receiver ring has been decrested/surface ground, you may indeed have to shim the front base. I had to on a VZ-24 that I recently completed.

I'll have to check that out. I'll let you know what I've found. smoker1

Mauser rings are frequently of various diameters and bases often have a little variation to them. I had a set of bases that were so far out I did not even bother figuring the shim.

This is one of the main reason I have stopped buying "production" bases. Too much variation.

So without more information I would not say your gunsmith is out of line.

So far I have only seen the rear ring sitting on the rear base with no scope but by eye it looked like there would be enough room under the front of the scoe to throw a barn cat through. Course my eyes are old

He could go with a one piece base, that way the rings will be on the same plane. But, the one piece might still require shimming, depending on how much adjustment the scope has. And yes, I know some people consider one piece bases to be rather butt ugly.

I suggested one piece base as that is pretty much all I use now. I would figure with all the years that the Mauser action has been modified, full raced, etc. that all the problems would have been ironed out.

There are ways to tell if the bases need shimming, but with out pictures and details, how are we to guess as to why or how much? Those are the questions your son in law should have asked the gunsmith who did the drill and tap work. It's nothing that can't be overcome, once the problem is figured out.

It's actually pretty normal. Some bases now come in a package that states that shimming may be required. Brownells carries shims to fit normal hole spscing. A lot of bases aren't shimmed which should be. I have seen many base/action combinations which used up half the elevation adjustment of the scope to get in the ball park. As mentioned, cleaning up a military action will often cause a misalignment.

The gunsmith said .030, but when we get my 1" piece of rod stock in the rings it will be impossible to tell. smoker1

Weaver bases for Mausers use a #46 for the front base on both models. The rear base for a small ring is #55 and #45 for a large ring. The curvature of the rear bridge varies greatly amongst different manufacturers. Many times the rear base will only rest on the edges and not the center of the base. You will need to re-contour the rear bridge or the bottom of the sight base to match. If this is the case, shimming the front base is not the answer. If the receiver has been ground, you will need to shim. This is all normal for Mausers. Use spotting color on the bottoms of the bases to confirm even contact on the receiver.

quote:

Originally posted by craigster:
He could go with a one piece base, that way the rings will be on the same plane. But, the one piece might still require shimming, depending on how much adjustment the scope has. And yes, I know some people consider one piece bases to be rather butt ugly.

The problem here is if he goes with the one piece and the bridges are off, he will only warp/bend the one piece base when he tightens it down.

Why not just put a straight edge across the bases to see if they are parallel? If it is off that far and he is sure he has the correct bases, my solution would be to either glass the bases to the receiver or better yet, to glass the scope to the rings.

Sounds to me the the smith knew what he was doing and figured it out for him, ie .030 shim. You can get shim stock in kits from brownells. Still should be checked with a straght edge after shimming. Or glass the bases like Jim suggested. Lapping the rings or using rings with the alginment inserts would be a good idea too.
Don

If it is .030 off. Can that much be taken off the rear base instead?
and don't forget the screws.

Us a set of steel weaver bases (Grand Slamm/Warne).

You could re-machine the bottom base, but for the money...

Or you could grind .030 off the rear ring... again... for the money...

Thanks guys, I hate doing things once removed. I will see the Boy this weekend and get more info. I told him that there is no sense in investing custom money when you have a gun that will not shoot.His intent is to keep the barrel that is on the rifle. Keep you posted. smoker1

Watch this to solve a ton of issues

http://www.youtube.com/watch?f...ilpage&v=2BNDPNC4ELM

quote:

Originally posted by Smoker1:
I would figure with all the years that the Mauser action has been modified, full raced, etc. that all the problems would have been ironed out.

Let's see, the action was never designed for scope use. There were probably 100 plants at least making 98 pattern actions. Some which were scrubbed and given all this variation you expect a mass produced base(s) to be a drop in fit? Can't happen. Heck, many much more modern commercial rifles still require shimming with mass produced scope bases.

Regardless, there are many pretty easy ways to correct the problem to include shimming, recutting the bottom of the base, Burris ring inserts, and custom bases.