FN Mauser scope mount problems / questions

Discussion in 'Gun Project Questions & Gunsmithing' started by Lefty Trigger, Dec 6, 2017.

  1. Lefty Trigger

    Lefty Trigger

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    I have a pre-war FN 98 Mauser that my dad modified back in the late 60's. This gun was in my sisters possession and neglected until I acquired it last year. The stock was cut down to fit a small child and I had to restock it for an adult. I found out that the front sight was knocked off (pulled threads out of barrel) an glued back on, thats right glued! I had the rear sight removed and the action drilled by a smith that I was referred to by my local gun shop owner for mounting a scope. Here's where it goes horribly wrong. This guy is no more a gunsmith than goober at the filling station. The mounts are crooked and not even on the same plane! Not to mention way too far apart. If you put just the front ring on and lay the scope in it the scope point way to the left and it gets worse with both rings installed. No way your going to "lap" these in they would have to be line-bored to correct this much error. In the pictures you can clearly see the front mount holes are not square to the barrel and off to the right. I'm thinking my only solution is a one-piece picatinny rail and hoping the screw holes wont overlap and redrill the action. Could this be a solution? Is there a one-piece rail for a 98 Mauser large ring?
     

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  2. Riesel

    Riesel Gold $$ Contributor

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    I experienced a situation quite similar to yours recently. I'm not sure if this will work but this is what I did.
    I got a scope and centered the recticle to be exactly in the center both horizontally and vertically. I have a V-block device that I use for this. There is a one piece picatinny rail for the Mauser 98 and it has only one hole in the rear and is designed to fit over the stripper clip hump be it there or not. Hopefully, the front screw hole is correct. You should be able to discern this visually and by measuring. Install the one piece rail using only the front screw and attach rings and "centered" scope. I then used a Bushnell collator (is that the right word?) bore sighter and moved the rear of the rail to center the vertical line (windage). I marked the rear rail hole and the second screw hole in the front, removed rail to see what I had. The rear was in a completely different location and the front was about a quarter screw size off. I used plugs with epoxy to fill in the old holes and file off the very top for a smooth finish. I did this on all three holes and then went thru the same procedure as above to remark, re-drill and re-tap the holes. I was able to sight in rifle with a reasonable amount of windage adjustments and it has held up well on a .308 rifle. It's a real pain in the butt procedure but if they had been drill correctly............................
    Second option might be, and this is a big maybe, a set of Leupold or similar Rings with the rear adjustment might get you there. With the rear windage adjustment and some ring lapping you might be able to get there.
    I hope some of this helps.
     
  3. Pheasanthunter

    Pheasanthunter Silver $$ Contributor

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    Egw has a one piece rail for them
     
  4. nicholst55

    nicholst55 Brass Whore

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    While I have seen worse, I think those holes could be TIG welded and redrilled by someone who knows what they're doing (and has a jig).
     
  5. Riesel

    Riesel Gold $$ Contributor

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    I'm with you on the tig welding and think that somone who really knows what he is doing can achieve this. I'm just a little nervous about heating up these 98 Mauser actions because of the heat treating, or lack of (surface only) that they received when manufactured.
     
  6. shortgrass

    shortgrass

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    Lefty, there is the possibility that the receiver is twisted. The holes may not be on the centerline, but it appears from the pics that the front 2 line up with each other, and the rear 2 line up with each other. IMO, and that is all it is,, is that a 'rail' does not belong on a '98. A good Mauser '98 will make a fine classic hunting rifle, but a 'rail', and worse yet a mag box hanging out from underneath just do not 'fit'. Another thing that needs to be mentioned; the front mount can only be moved rearward so far. You should not drill/tap into the top locking lug abutment. Nor should the drilling/tapping 'skim' the face of that abutment. It will weaken it to the point it may set back. Much of the Mausers' strength comes from its mass, the mass built in as part of the design. Some are case hardened very well, some are kinda' 'iffy' on their surface hardness and how deep that hardness is. Yours is obviously a military Mauser, as I can see the thumb cut in the off-side rail/wall. I recently repaired a similar situation for a customer, but it wasn't low cost by any ones definition. Every one of these "off the centerline" scope mount holes situations requires hands on examination to determined what the solution might be. Anything less is just speculation. Sporterizing a military '98 is a costly endeavor and I discourage those that would use them for a sporter from using them unless they are willing to spend some money,,,,, lots of money........
     
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  7. Gundoktr

    Gundoktr

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    This is a common problem that has happened a number of times, sad but true. I would suggest mapping the original holes and making a mount either custom or using Leupold gunsmith bases,. They can be set on the action in correct position and then drilled to match the mapped receiver. Not for the faint of heart but will end up satisfactory. Email me if interested: Jkob60@msn.com
     
  8. Lefty Trigger

    Lefty Trigger

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    The front mount is the one that is crooked. I could have lined it up with the crest stamped in the action and got it straighter than it is. It's a great old gun but the money value just is not there to spend a great deal on it. I did find the one piece rail from EGW that was mentioned above and that may be the simplest solution for the repair. I have an appointment with another smith that said he can weld the holes and make the repair but like you said he wants to see it first.
     
  9. watercam

    watercam Silver $$ Contributor

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    A non-Tig welding fix is to epoxy screws in the holes and re-drill and tap. Just as strong with no heat treat issues. Done it many times with no issues down the line.
     
  10. fyrewall

    fyrewall

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    Sure sounds like a challenge.

    My best idea would be to find a spot on top of the receiver ring that did not have a hole and would allow some type of 1 or 2 piece base to be positioned over that spot and have enough receiver ring without a hole to drill a second hole using the other hole on the front base, avoiding the abutment where the bolt lug locks up - drill over the bolt lugs (as mentioned). The same for the receiver bridge. New holes front & back. All existing holes appear to be funny, like wandering holes.

    My experience with drilling holes that are touching holes that have been welded shut is that upon drilling the drill drifts into the welded hole because of the differences in steel hardness or even drifting into a softer steel screw and other stuff. I believe 98's have a real hard surface.

    I would select a rotary dove tail mounting system with opposed rear windage screws and then use Burris Signature rings that have those nice eccentric ring inserts. Most 1 piece bases of this type only require one hole in the rear receiver bridge. The stripper clip slot hump has been ground off. A variety of M98 bases are available

    I am an old guy who was around when surplus (excellent to terrible) M98's were around for real cheap prices. I use pop can aluminum, about .005 thick for shims on my Mauser actions to fill the gap between base and bridge when the base is cinched up tight against the front ring. A more respectable & professional job would use epoxy bedding only bonded to the base. The exposed pop can aluminum layers don't look too tacky upon darkening them with the Birchwood aluminum black stuff.

    These are neat old rifles should they be able to talk could tell quite a history. Your Mauser appears to be one of the better ones. The crest on the ring looks like some South American country. Give the receiver a hardness test, this should leave a small indent near the receiver recoil lug. Save $$, use what is available.
     
    Last edited: Dec 7, 2017
  11. kendog

    kendog

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    I wouldn't TIG it. Put it in a Forster jig and find the bad holes. Might be one, might be all of them. Tin some long 6-48's with Hi Force 44 solder and sweat them into the bad holes. Pay attention to the depth of each hole. Trim/file them off to the receiver contour, set the barreled action back up in the Forster jig and put the new holes where they belong. If you are careful, you dont even need to take it out of the Forster for soldering and trimming/filing. Put some masking tape over the cut off screws to have a "stop" for filing. No need to nick the bluing.
     
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