Need tap and thread advice for my Mauser...

[TankHand]

So I inherited my grandfather's sporterized .30-06 Mauser that meant the world to him, therefore me too. I mounted a modern scope on it, and replaced the two-stage military trigger for a timney unit, and glass-bedded it's action. It shot like a dream. Then to make things go bad, I started going through a gradual succession of different optics, and managed to lose a screw that holds my rings together.
Let me back up. My modern scope (1st attempt) was in the form of a Leupold VX-1 4-12x40, and I had to get the front mount shimmed up to adjust for height. I had maxed out the vertical rise on my scope, and was still shooting too high, and this was the gunsmith's fix. The mounts, I am told are Sako mounts from 40 years ago, and the screws are of a funny thread that isn't quite metric, or standard. I went to a new gunsmith, who promptly put two of the wrong screws in, and boogered up two of the threaded "holes." I then went on to screw it up further by mistakenly forcing these into other holes, and I am since left with like 4 (out of 8) holes that have bad threads. I guess what i'M asking is if anyone has experience enough with scope mount screws, or any gun screws for that matter to steer me toward a good tap and screw option that will be available for me to fix this problem and come out with 8 uniform holes, each with the same threads, and screws?

Any help is greatly appreciated; I will try to get a thread count, and diameter with a guage. I's say that the threaded shaft is about 1/16th -1/8th in diameter. The screw heads are shouldered, and have only a slotted screwdriver head. They are about 3/8" long. Unfortunately, I don't have a tap set, and will either have to buy one, or rent one if I can find the correct size to move into for a proper set of screws.

 

[rcmodel]

Not many American gunsmiths or hobbiests had metric taps & screws when your gun was put together.
Very likely the orginial screws are 6x40 or 6x48TPI.

You could try re-tapping the holes and see if they will clean up.

Or you could drill them out and tap them 8x40TPI.

Both Brownell's and Midway have a complete line of taps and scope mount screws.

rc

 

[feedthehogs]

Take one of the good screws to a machine shop to size for you.
You can buy individual taps for a few bucks but don't get crappy dime store taps as they break easier as the hardening is either not there or suspect.

A T handle tap wrench works best as it allows you to put downward pressure on the tap evenly. An adjustable wrench tends to put the leverage off to the side leading to cross threading.

Taps that small can be broken easy and since they are hardened they are about impossible to remove if bound in place.

Take your time use tapping oil and if the threads start to feel tight, stop back out tap, clean metal out of tap and hole and proceed again.

 

[rcmodel]

Good advice.

I should have said the same thing.

If you have no experience with tapping threads, a hard & tough Springfield receiver is not a good place to practice on!!

You would probably be ahead of the game to take the rifle to a good gunsmith (not the one that screwed it up in the first place) and have him resolve the problem.

Even machine shops are not usually equipped to handle 6-48 & 8-40 gun-screw thread sizes as they are not the normal SAE thread sizes commonly used in machines.

rc

 

[TankHand]

Thanks for the help...

I'm appreciative of the advice. The holes are in the rings themselves, and not the receiver. I have had experience tapping holes before, but mostly into aluminum, for heli-coils. I will take the screws to a machine shop like you suggested, but what is a good source for a quality tap? Napa? Again, thanks for the help.

 

[Jeff82]

Brownell's

 

[jimmyraythomason]

a new scope mount and rings will cost less or at least close to a quality drill and tap set.

 

[Riss]

Use a t-handle in a drill press. Not for the motor, but to hold everything straight and if you loos at a good t-handle it has a small hole above the tap, as does the tap itself for a center. Use the center, held in the drill chuck, to keep downward pressure while you hand turn the tap handle. Makes it work similar to a tapping jig.

 

[MichaelK]

Use a t-handle in a driss press. Not for the motor, but to hold everything straight and if you loos at a good t-handle it has a small hole above the tap, as does the tap itself for a center. Use the center, held in the drill chuck, to keep downward pressure while you hand turn the tap handle. Makes it work similar to a tapping jig.

That's how I tapped my Mauser, in the drill press. It will hold the tap more securely then you can ever do by hand and the chance of breakage is much less.

I would add one suggestion though. As you rotate the wheel to drop the tap into the work, you are exurting downward pressure to feed the tap into the reciever. Be carefull taking the tap back out, by continuing to apply some downward pressure as you screw the tap back out. I ruined the top portion of one thread because as I withdrew the tap, the spring tension on the chuck yanked out the tap at the last turn, ruining that first or second thread. Once I got around to sighting in that rifle, that's the screw that stripped out upon firing. Had to come back and drill and tap the hole to a bigger thread to get a secure screw.
Michael

 

[BADUNAME27]

MSC industrial carries high quality taps. For this application I would use a 4 flute starter tap because none of the holes are blind.

Castol Moly D is some of the best tapping fluid out there. GET SOME as gun receivers are made from tool grade steels. They generally love to eat taps and make a mess of things if a guy isn't careful.

DO not buy import taps. Spend the extra few bucks and get ones made in the states. You don't need through tooling coolant delivery as your not using a production CNC, but a coated tool will certainly work better with the material types typical to guns.

As for your Mauser. Someone mentioned an 8-40 screw and that is an excellent choice. Use a #29 drill (.136") or if the material is really nasty use a #28 (.1405"). It's always best to drill using a fixture of some kind. a drill press at the very least, a vertical mill is certainly preferred.

Good luck.

C

 

[Zeke/PA]

TankHand,
I would be glad to repair these rings for you free of charge, you pay postage both ways.
I know that this sounds like B.S. in this day and age but in reality what do I have to gain from a set of buggered up rings.
Contact me.
Regards, Zeke
P.S. I am a Journeyman Toolmaker with formal training as a Gunsmith.
I would be more than happy to assist you.

 

[a5werkes]

3 Cheers for Zeke/PA......

That's the kind of gunsmith fellowship that makes this forum a great fraternity indeed.

 

[TankHand]

Thanks all around. I seem to have found the good guys on the internet here. I have actually found the answer to my problem here, in the way of a company called fastenal, out of Houston. Turns out that my rings were European, and the mounting screws are in fact "M-3.5" which is an odd-ball for a cheesehead screw. I spoke with a gunsmith here in Beaumont yesterday, and we exhausted his supply of Brownells' screws trying for the right thread, and he put me on to these guys. They have ordered the screws I need, and I'll keep you all posted on how it turns out. Thanks to Zeke for such a generous offer, I may still have to take you up on that, but I'll try everything I can here first. Thanks again everyone, and God Bless.

 

[nicholst55]

Good on ya, Zeke/PA!

TankHand, be sure to let us know how this turns out.

 

[TankHand]

All is well so far...

Got my zinc coated screws from fastenal, and they are panheads, and don't fit in the recesses of my rings. They are tight though, and seem to be holding their own. If anyone knows a source for Metric 3.5 hardened "cheese-head" screws, please let me know. I am already checking ebay.

 

[Jim K]

You should be able to turn the heads down. If they are not too hard, you can use a drill press and a file.

Jim