Mauser 98 weaver scope base help


March 1, 2013, 06:58 PM
I have a mauser M48A action that has holes drilled for a weaver style scope base. The rear holes (closest to the shooters face) do not match the standard Weaver base # 45. The holes are too far apart to fit this base. The distance between the center of the two holes is about 13/32, actually looks to be 3/8. I am trying to identify a weaver base that will fit these pre-drilled holes. Can anyone help me? Thanks!

I have been looking on-line but I would probably order 4 different bases and have none of them match with my luck! :banghead:

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March 1, 2013, 10:18 PM
I fear that you won't find a base that will work. The Weaver 45 will barely fit on the rear ring. I am not aware of another base that has a greater hole spacing that will fit the available space.

March 1, 2013, 10:32 PM
I actually need a base that has the holes closer together than the weaver 45.

March 2, 2013, 01:40 AM
I think it may be drilled for the Leupold 98 Mauser 2 piece base that fits over the charging clip hump, if the holes are that close together. my best guess with out seeing it.

March 2, 2013, 01:52 AM
Here it is. The front two holes fit the weaver 46 perfectly. The back two (on the left in pic) are to close together for the 45:

There are also two holes on the right side of the rear of the receiver which i can only guess was for a lyman peep sight.

March 2, 2013, 08:51 PM
Anybody have a large stock of weaver bases they could measure the holes on to see if they are 3/8 apart? Please need some help on this one. More problems than I anticipated for this build!

Jim K
March 3, 2013, 02:51 PM
If you can't find an exact fit, you can buy a long Weaver base with the holes widely spaced, drill a new hole in the base as necessary and then cut off the excess.


March 3, 2013, 04:39 PM
Jim- awesome idea! This can solve it for me! Thank you sir!

March 3, 2013, 06:14 PM
This is a guess but a base with 3/8" (.375") hole spacing is Warne Maxima 2-Piece Steel Weaver-Style Scope Base Remington 799, Interarms Mini Mark X, Charles Daly Mini Mauser Gloss. Here are the specifications:

Package contains two bases. First is .960 long with .625 hole spacing (center to center), second is .830 long with .375 hole spacing (center to center). Product photo shows longer base where slot is offset toward one screw hole. Shorter base has slot centered between the two screw holes.

The rear Weaver equivalent would be a Weaver Top-Mount #23 Weaver-Style Rear Scope Base Remington 799, Interarms Mini Mark X, Charles Daly Mini Mauser Gloss. So my guess would be a Weaver #23 base for .375" center to center hole spacing.

I like Jim's suggestion as I have done that also.


March 3, 2013, 06:20 PM
I'm with MR. I think it is a drilled for a Leupold or similar.

March 6, 2013, 03:47 PM
well the hole spacing on the weaver 23 mount, but the base is machined for a smaller action than the large ring m48. Not sure what to do now. The only other thing I can think to do is drill and tap a new hole for the original base. do you think it would weaken the rear of the action to much to put a third hoke on the top?

March 6, 2013, 08:16 PM
Probably won't hurt, but I would not do it without exhausting all other possibilities. As I noted, it looks like a Leupold hole spacing. Measure carefully and check with Brownells tech support. If you stuck on Weaver, drill another hole in the sight base and save that receiver from further abuse.

March 7, 2013, 04:36 PM
Well I called brownells and they said the hole spacing is .325 and the actual holes in the receiver seem to be about .400 apart at center so I am leaning towards cutting a new hole on one of the weaver mounts I have.

March 8, 2013, 12:47 AM
I am a walking Mauser Junk yard, starting in 1965, but really got going in 2000.

I buy Mauser that are screwed up, just for parts.
The usual screw up is the scope mounts.
I waller over the hole, the countersink, and the concave radius on the bottom. I shim and glass bed so that the mounts are co planar and parallel with the bore. [ or pointing 20moa downward if we dress up and play sniper]. Notice the boring head marks on the bottom, ala Steve Ackerman.

March 8, 2013, 09:29 AM
Clark can you elaborate? I am not sure what you are suggesting.

March 8, 2013, 01:35 PM
When holes in the receiver don't match holes in standard mounts [base] or are off center, one can:
1) Drill and tap more holes [Swiss Cheese solution]
2) Weld over the holes and start over [Nuke option]
3) Make a custom mount [ all day long option]
4) Screw something down and lapp the rings [wreck the rings]
5) Modify the mount [ mod the cheapest part]
6) Don't get involved

I have been going for option 5)

To modify the mounts [Brownells calls them Weaver bases] I have modified a pair of V blocks.
Those hold the mounts by the edges.
I move over [make oblong] the hole with an end mill the same size as the hole.
I move over the countersink with an end mill the same size as the countersink.

I change the bottom radius height, radius size, or centering with an end mill [if there is one the right size] or boring head.

The alignment procedure starts by centering a reticle in a scope body. I used to put a scope in half rings and rotate, and then adjust the elevation and windage until the center of the cross hairs stayed on one spot on the target. Now I press the objective against a mirror and adjust until the two cross hair images over lap.
Then the screws to the mounts are put in loose. The scope is shimmed [with narrow stacks of tape] until the centered scope bore sights. Then wet epoxy is put between the mount and receiver. The scope is checked for bore sight again. When the epoxy hardens, the screws are removed, threads are cleaned, and the screws are tightened with loctite.
The scope should then be sighted in when centered and no ring lapping needed or desired.

March 8, 2013, 01:57 PM
Leupold sells "gunmaker" bases for just that purpose. Drill yer own holes. Machine yer own radius. Clark's method of slotting the screw hole and countersink is going to be your fastest, safest, cheapest solution if you cannot find a base with the correct c to c spacing, bottom radius, and height. Beats the heck out of putting more holes in the receiver.

March 8, 2013, 02:29 PM
My problem is I do not have access to milling machines to do the work for something like that. If I could cut the radius I would be set because mini Mauser weaver 23 is perfect for the hole spacing, but the radius cut is not shallow enough to match the large ring radius. Right now I am leaning towards either cutting a third hole, or using a base and trying to drill a third hole in the mount fixture. Mostly because those are the only two methods I have the tools to do correctly. Thanks for all the details Clark!

March 8, 2013, 03:23 PM
Got a drill press and a way to securely clamp the base while you drill it? I would not normally suggest using a drill press, but a decent job can be done on a simple hole and counterbore. Or why not take it to a machine shop and have them modify the base? Heck, I could probably do it with a rat tailed file and a hand drill in a pinch. Still, the hole spacing is only half the battle. You have to ensure that the base height is correct for vertical ring alignment. Just grabbing any old Weaver base and poking holes in it ain't gonna get you there. Even the ones made for that action must be checked due to the variations in the actions.

And I'm curious how you are measuring. You first say "The distance between the center of the two holes is about 13/32, actually looks to be 3/8", then "about .400" apart." Do you have dial calipers, are you measuring between the screws, and adding one diameter? I do not wish to offend, but the whole thing is beginning to sound like you are over reaching your level of understanding, skill, and equipment.

March 8, 2013, 07:13 PM
BBBBill - I think you are right about me being out of my league on this task, but I think I can find a solution. So each hole is .14 in the distance between the outside edges of the holes is .530 in. The distance between the inside of the two hole edges is .250. That would mean the distance between the center of the two holes would be .390 in.

Jim K
March 8, 2013, 08:31 PM
Measure the receiver holes center to center with a plain old caliper.

Set the caliper centered in the hole already in the mount. Using the caliper, scribe a cross line on the base where you want the new hole. With a pointed tool, scribe a lengthwise line in the center of the base. Where the lines cross, center punch a drill guide hole. Using the right diameter drill, drill the mount for the small diameter. Using a larger drill, countersink for the screw head.

Any small adjustment needed can be done with a small round file or a Dremel tool.


March 20, 2013, 01:54 PM
Ok well the Leupold two piece STD mounting system did not fit. I spoke with brownells customer service and I believe that the one piece Leupold base should fit. I am waiting on that to arrive before I attempt to modify the weaver 45 mount. I will let you know how it turns out!

March 28, 2013, 07:50 PM
Well the leupold one piece base did not fit either. The back screw hole is just a hair further back than the rear whole in the base. Well now I am out of ideas, can anyone help?

March 28, 2013, 08:29 PM
Buy a blank and drill it or get one way oversize, cut it down and drill it. That is all I can come up with.


March 28, 2013, 10:13 PM
Not sure what blank would fit the rear of a Mauser 98 large ring type.

March 29, 2013, 07:03 AM
You get a blank like this one ( as an example, then mill and drill. See Clark's post #16 in which he includes images.


March 29, 2013, 06:06 PM
Don't have access to a mill :(

March 31, 2013, 02:16 PM
Was able to use a dremel and got the scope base to for. Had to trim off the corner of it and the scope mount base, but it seems to work. Thanks everyone!

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