View Full Version : Drilling and tapping for a scope

March 12, 2012, 02:19 PM
I have a sporterized 1891 Argentine with a great bore I use for deer hunting. I want to be able to mount a scope on it without using a LER. I'm not a stranger to drilling and tapping from doing automotive work so that doesn't concern me. What I'm wondering is were exactly do you place the holes on the receiver?

March 12, 2012, 04:21 PM
Where they are needed ;). Buy the correct mounts for your receiver, find the centerline, position the mounts, center punch through the holes in the mount.

March 13, 2012, 10:02 AM
[were exactly do you place the holes on the receiver?]

Everybody, except Bubba, uses a drilling jig of some kind, like the Forster or B-Square, to ensure the holes are plumb/square with the receiver's bottom flat AND in the correct location(s).


James K
March 13, 2012, 01:47 PM
The way some folks describe it as being so simple (no jig, no milling machine, no drill press, just scribe a line and have at it with the handy 1/4 inch hand drill), I wonder why so many people mess up.

I have drilled and tapped a lot of receivers and I wouldn't try it without a jig (though there are exceptions, like a side mount).


March 14, 2012, 01:53 AM
1891 Argentine should be a flat bottom receiver.
Use your calipers as accurate jaws to hold your mount on the top of the receiver to get center position after you remove the loading hump.
This link should help. I use this method on Mexican, Argentine, Spanish, Turkish, and others.


March 14, 2012, 09:57 AM
I have never seen a drilling jig for an 1891 Argentine Mauser... I've seen them for the K98/large ring. Also I've seen the cost for said drilling jigs... And not being a gunsmith it's hard to justify buying a hundred dollar jig for one receiver, one time...

I wouldn't be tackling this ordeal with a 18v Milwaukee or anything like that. I have access to a drill press I would use if I knew exact hole placement for the mounts.

James K
March 14, 2012, 02:31 PM
If you can't use a jig, then you can try this.

Get some clamps.

Clamp the receiver solidly to the bench or in a vise. Use a machinists level on the bottom of the receiver to make sure it is level.

Clamp the mount base to the front receiver ring. Check to see if one hole, if drilled too deep, will go into the chamber. If so, make note of that.

Put the machinist's level crossways on the top of the mount. Move the mount base until it is perfectly level. Center punch through one of the base holes, lightly. Double check everything, including using a long straight edge in place of the level. Triple check. Twice.

Then center punch the other base hole. Double check. If all looks good, including by eyeball (it is surprising how accurate a trained eyeball can be), center punch normally and drill ONE hole in the drill press. MAKE SURE you don't drill too deep and drill into the chamber.

Screw down the front base with one screw and mount the scope with just the front base. Set the rear base in place and try the scope. (You are checking for mismatched bases before going any further.) Double check, etc.

If all is OK, remove the scope and the front base, and drill the other front base hole. Double check. Again. If all is OK, repeat the process with the rear base.

Make sure the bolt works; if not, you might have drilled into the bolt lug area behind the chamber and the screw is blocking the bolt from turning, or a rear base screw might be keeping the bolt from going into place. If so, remove the offending screw and shorten it until the bolt clears it. (Do not grind off the locking lug to clear the screw, as I heard of one fellow doing.)

Lotsa luck!


March 14, 2012, 02:33 PM
Do not grind off the locking lug to clear the screw, as I heard of one fellow doing

Thanks, you just made my day.

March 15, 2012, 08:10 AM
Thanks James!

Do not grind off the locking lug to clear the screw, as I heard of one fellow doing

Made hot coffee come out my nose... thanks...

March 15, 2012, 06:27 PM
To amplify what James K said...as most people aren't familiar with a machinist's level, the thickness of a piece of paper will throw the bubble completely off the scale. See this: http://www.starrett.com/metrology/metrology-products/precision-measuring-tools/machinists-levels
The cheapest route here is to take it to a gunsmith, and yeah, it may cost a few bucks for him to do it. But his cost to do it will be much cheaper than his cost to fix what you screwed up by not having the proper tools. This assumes that it IS repairable.

James K
March 15, 2012, 06:56 PM
I usually recommend a gunsmith but some folks just insist they want to do it themselves, without spending money on a jig. The method I described will work.

If the idea of grinding the lug to clear the screw results in coffee in the nose, how about the "gunsmith" who didn't know about short chambered barrels, so he ground the back off the locking lugs. When questioned, he didn't understand what he did wrong, as the headspace checked OK with the gauges. Of course the back of the cartridge case would have gotten a bit cold, sticking out in the air like that, but what the heck. (Fortunately, someone else checked the rifle before the customer fired it.)


March 16, 2012, 08:22 AM
I am familiar with the machinist's level and own one (use it for checking heads and engine block decks).

I have been considering a gunsmith but I enjoy doing this kind of stuff. I'm the same way about my cars... I don't let anyone else touch them... The thought of another man/woman with their hands all over my Z28's engine makes me shake.

James K: That one didn't make the coffee go... but it did make the head shake.

Harry Bonar
March 16, 2012, 07:36 PM
The best base for the Mauser is the Redfield one piece base for the military mauser - you don't need to recontour the rear ring that way.
Harry B.

March 17, 2012, 07:34 AM
To add to James K's procedure, I would highly recommend using a one piece base, further reduces the chance of error. I know some people don't like 'em but accuracy is paramount. Goat

March 18, 2012, 09:04 AM
Some folks use hot glue to help holding the base for drilling. I used super glue and then cleaned it. Hot glue maybe a better way to go and easier to clean. Bore sight before drilling. Once drilled, no return!