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Redrilling/tapping slightly cockeyed 6-48 holes to 8-40?

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  • Redrilling/tapping slightly cockeyed 6-48 holes to 8-40?

    So I'm 90% done building a rifle on a Savage 10 action...
    Only to find, now that I AM 90% done with barreling, action work, restocking, etc.. .that the rear set of scope screw holes and the front set of holes don't quite share the same centerline. Oops. (the factories oops, not mine... not that I've never done that... but I digress).

    I haven't measured the precise distance that the holes are offset from each other, but it's no more than the thickness of a 6" steel rule.

    So I'm thinking...
    How to bore/drill NEW holes over the top of the old ones - from 6-48 to a larger 8-40. (this assumes that after I'm done measureing, that the diameter and location of the new holes does not leave part of the old holes peeking out).

    Plug screws in the old holes, stub drill #29 and tap?
    Or leave out the plug screws, and HOPE that the drill is rigid enough NOT to follow the old hole...
    Unfortunately, I don't have an end mill of .136", nor a carbide drill... so those are not presently options.

    Any input appreciated!
    Paul F.

  • #2
    Point of View

    From my own point of view, I would go with plugging the hole with a soft steel 6-48 "plug" and re-drilling it in the correct location. To me, if you try to redrill the existing hole, there is large possibilities of the drill following the old hole and breaking off in the hole and then there is a REAL mess to clean up. Ideally the plug could be silver soldered in place but then do you really want to heat the receiver? I would suggest using Permanent Grade Lock-Tite on the plug when you plug the hole. That should hold it in place while the new hole is drilled and tapped.

    Just my $0.02.
    Bill

    Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

    Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

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    • #3
      Plug them. A drill will always take the path of least resistance.
      Jon Bohlander
      My PM Blog

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      • #4
        Plug the holes using Loctite on the screws. When it's cured, instead of drilling the new holes for the 8-40, find a metric center cutting end mill in 3.5mm, and plunge mill the holes for the tap. You're only talking a .0018" size difference, after all. Or, use a 9/64" end mill if you can find one.

        David
        Montezuma, IA
        David Kaiser
        “You can have peace. Or you can have freedom. Don't ever count on having both at once.”
        ― Robert A. Heinlein

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        • #5
          Two Options

          I shop for DHT Springfields in pawn shops. The DHT ones that have been D&Ted usually have the holes crooked. If the greater diameter of a #8 screw will clean up the hole, the easiest method to fix the problem is to plunge cut with a 9/64 endmill and tap for #8 screws.

          The other option is to make bases to match the rifle. I usually do both as bases for Springfields that take #8 screws are hard to come by.

          I'b be willing to bet a Savage receiver is not as hard as the bridge on a DHT Springfield. This should be an easy fix, and you will end up with the advantages of the larger screw size.

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          • #6
            DHT= double heat treat?

            Comment


            • #7
              Thanks for the replies!

              I like the idea of boring the holes with an end mill..
              Unfortunately, I dont' have an R8 collet for a 3.5mm.
              I DID, however, find that 9/64" end mills are not difficult to find at MSC :-)

              I don't really have the option of moving the holes if I want to use the already purchased one-piece base... (ironically enough, the 9/64" end mill, and a counterbore to open the holes in the mount from 6-48 to 8-40 will probably cost what I have into the mount... but I LIKE this mount!).

              Next time I take this rifle to bits for more fitting (the safety still won't engage after a new trigger, and I have some more fitting on the detachable magazine to do..). Pesky tuning, but not as pesky as measuring the proper hole spacing and alignment, and boring new holes.

              THanks again for the replies!
              Paul F.

              Comment


              • #8
                Scope mount holes out of alignment is quite common on older firearms . It's probaly why they invented the standard mount. As for redrilling the existing holes I think there's a good chance your going to trash your reciver.

                Comment


                • #9
                  Counterbore

                  Dial in your existing mount hole and counter bore with a 1/4 endmill. DHT= Double Heat Treat. Fishbait, congrats on a nice, upbeat, positive first post.
                  Last edited by mike thomas; 05-16-2009, 10:58 AM. Reason: typo

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                  • #10
                    Originally posted by fishbait
                    Scope mount holes out of alignment is quite common on older firearms . It's probaly why they invented the standard mount. As for redrilling the existing holes I think there's a good chance your going to trash your reciver.
                    Yeah, if he were to use a drill. An endmill will clean up and straighten the holes because it does not use the existing hole as a guide.

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                    • #11
                      I'm thinking this guy might not know what a standard mount is or what it can do for him. Last time I bought one I paid $21.00 and it took 10 minutes to install. Do you really want to experment with a expensive gun when the obvious solution costs so little?

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                      • #12
                        I have seen literally hundreds of off center holes like this in Springfields and Mausers in the last 40 years...repaired in the manner already described. Put a proper length screw in the off center hole with permanent locktite. File or mill off the part of the screw that protrudes and polish, and touch with cold blue.. Then properly re-drill or use an endmill to put the hole where it belongs and retap. Once the mount is on, you will never even see the work and the scope mount will be properly mounted.

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                        • #13
                          I do question exactly what a "standard" mount is and how it can cause mis-drilled holes to move into line. I have scoped several rifles myself, have read gunsmithing books, magazines, advertising and catalogs for many years and never seen such a mount.

                          On the other hand, the plugging and redrilling of holes as described seems to be a very common fix to the problem and is quite often described in the publications mentioned.
                          Jim H.

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                          • #14
                            Originally posted by fishbait
                            I'm thinking this guy might not know what a standard mount is or what it can do for him. Last time I bought one I paid $21.00 and it took 10 minutes to install. Do you really want to experment with a expensive gun when the obvious solution costs so little?
                            "This guy" knows more than you think.
                            "This guy" has built more than a few rifles.

                            A "standard" mount doesn't do jack for misaligned holes. Not to mention that, but a "standard" mount doesn't have a 15MOA slope for this project either.


                            Thanks to all for the HELPFUL replies (I do not include mr chum.. or fishbait, or whatever, in that thanks).

                            I have some tooling on order for the boring, and to redrill and countersink the mount.

                            Paul F.

                            Comment


                            • #15
                              There are a few mounts that will allow slight misalignment of mounting holes, as it will happen.

                              I am working with some 50's & 60's vintage guns and have been using Buehler mounts. They do provide for windage adjustment of the scope. I believe current Leupold mounts offer the same feature. There might be some others, none come immediately to mind.

                              In the same vein, I am looking for a set of Buehler 1" high rings, or at least a front high ring I do have a rear one and a front low to trade if that helps.
                              Jim H.

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