What Scope Base?


February 11, 2009, 11:27 AM
I need help figuring out what scope base to put on my Mauser project rifle. I had the gunsmith drill and tap it for a two piece base. I'm wanting to put Leupold bases on it and looking at them in the store, they're differentiated by manufacturer, like Rem, Savage, Browning, etc. I don't know which ones to use for my gun. The gunsmith that originally drilled and tapped it, passed away shortly after doing the work, so calling and asking him is out of the question. He ground down the charging hump on the rear of the receiver so I could use modern bases instead of having to use regular Mauser 98 bases. The front holes are spaced wider than the rear holes. I don't have a caliper to get exact measurements, but I used a tape and got pretty close. The front holes are 7/8" center to center and the rear holes are 1/2" center to center.

I'm really hoping someone can work with this information and help me figure out which bases fit my holes. Thanks!

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February 11, 2009, 01:59 PM
Just use the Mauser bases. Here:http://www.midwayusa.com/Search/Default.aspx#Base%20mauser____-_1-2-4_8-16-32

February 11, 2009, 02:04 PM
A friend told me that the FN Mauser bases is what I should use. Leupold makes a set for the FN Mauser so I'm going to end up picking up a set of them. These are what I'm talking about: http://www.midwayusa.com/viewproduct/?productnumber=580541

If those won't work, which specific ones will? I want to stay with a two piece set.

February 11, 2009, 02:24 PM
If that doesn't work and you have a non-typical pattern then go to the local gun store (a small one not a chain store) and the guy behind the counter will likely go through every one he has (I even had a guy pull his off his own gun -rings in my case- to see what would work for my issue) to help you out. That is the best I can tell you. I have never measured mine to say and the smith mounted the bases for me.
However the fact that the charging hump was removed leads me to think this one might be the one he was planning for you.http://www.midwayusa.com/viewproduct/?productnumber=285665 The review relates something to that effect, and the "different size could refer to either the difference in the height of the front and rear of the receiver, or the bolt spacing.

February 11, 2009, 02:35 PM
I personally like the mounts by Talley. They are light weight and the base and ring are one piece.

February 11, 2009, 02:52 PM
Here are the Talley mounts.

February 11, 2009, 06:33 PM
I picked up a set of the Leupold 2 piece for the FN Mauser like I had posted a link too earlier. They match up with the holes perfectly. The only problem is that the rear base protrudes past the end of the action and the bolt hits it pushing forward, preventing it from being lowered. It's a pain in the backside, that's for sure. So I ended up just spinning the rear base around. It moves the rear ring slightly forward, but only 1/8" or so, not much. After doing that, that portion protrudes into the cartridge opening slightly, but not enough to affect anything. You can still get shells into it with no problem. I'll have to take some pictures of it tonight and show what I mean.

FYI...I had to go with the high rings. The 44mm objective with medium rings rested on the top of the barrel. Parallax adjustment couldn't be used. So if anyone else does something similar. Just go with the high rings to begin with.

Friendly, Don't Fire!
February 11, 2009, 06:40 PM
It sounds like you have the ultimate setup now!

Use a bit of Blue Loctite on each of the screw threads after degreasing them with rubbing alcohol.

A little Loctite goes a long way!

February 11, 2009, 10:02 PM
Well now I might have another small problem. I got the scope all mounted and used a bore sighter to get it close. I got the windage set, but I was really low on the elevation. I adjusted it and I ran out of threads on the elevation knob. I'm still probably about 4 inches low for center with the bore sighter. What do I need to do about this? I've never had this kind of a problem getting a scope bore sighted.

February 12, 2009, 12:11 AM
Assuming (and we know what assumptions can lead to) that the scope bases are supposed to be level before mounting the scope, I would suggest the following -

1. Rig a cleaning rod parallel to the bore (A jag or brush takes care of one end, but the other may have to be made larger with tape to be roughly centered) and protruding 12" or so.

2. Use a torpedo level on the cleaning rod to level the rifle in a padded vise.

3. Now check the scope bases with the level.

If the scope bases aren't level, you solved the hole-spacing problem, but not the height of the two ends of the receiver bridge. You may have to have a machinist take the high scope base down appropriately so they will mount level.

February 12, 2009, 05:33 PM
Well hole spacing is no longer a problem. I found bases that fit the holes. Just the elevation deal is making me scratch my head. Would it be easier to machine down the rear base or to shim the front one up higher? I don't really know what to do about this. I've mounted a lot of scopes and I've never had this problem.

February 13, 2009, 11:02 AM
Have a gunsmith check the rings with alignment bars. If they are in alignment replace your scope(a possible source of the problem). If you shim or cut either mount that are already in alignment you will bind the scope. Not good. I would just try a different scope first and see if the problem still exists.

February 13, 2009, 11:08 AM
If you can go to a one piece base then shimming the front is the easy solution. Cut a piece of soda can to fit underneath it. If the two piece is all you can use, you can lap or bed the rings to get the alignment right. I prefer bedding with JB Weld myself. It actually improves the holding power of the rings and it won't move at all.

February 13, 2009, 11:49 AM
I don't think it has anything to do with the scope. It's going on a Mauser action and the rear charging hump was ground down so it could take modern bases. I think I'll probaby end up shimming the front ring and see if that helps. I've had several people say that they get into problems like that when using high rings. One guy uses the Burris stuff and he says that Burris even provides shims for their stuff. I'll probably try a piece of aluminum foil or cut a piece of a soda can and see if that helps.

February 13, 2009, 02:45 PM
Brownell's has shim kits for that very purpose. I have mounted a LOT of scopes on Mauser M98s and have had a few minor alignment problems. Some had to be shimmed most didn't. Your scope is probably okay but it is better to test another scope than to spend hours modifying bases only to descover that the problem was the scope all along. It pays to check the easy stuff first.

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