Drilling holes for scope mounts

mickri

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One of my up coming projects is to rebarrel some mauser actions that I have. Part of these projects will be drilling and taping for scope mounts. On the rear of the receivers no big deal. You can drill and tap all of the way through. But the front mount is different. You have blind holes to drill and tap. First question is it ok to remove the barrel and then drill and tap all the way through like for the rear mounts? If that's a no no then how do you measure how deep you are drilling the blind hole?

Second question is how do you set things up to know that you are drilling the holes centered to the bore of the barrel? And I don't have the funds to buy a forester(sp??) jig to only drill a couple of receivers.
 
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First, let's be clear, I am not a gunsmith.
I use Weaver 2 pc bases entirely, on Mausers. My low budget home made methods are crude but work. Get a piece of 1" cold rolled or similar, 6 to 12" long, drill a dead true hole, 1/4" or so thru the long axis. This is your "peep sight". Attach your scope rings and bases, clamp the barreled action securely in a vise or vee blocks. Align the barrel bore, you're looking thru it, at a distant easily discernible object, put the "peep sight" with the bases and rings attached atop the action, adjust bases and rings as necessary so that the peep sight is aligned with the same "target'' as the barrel. Clamp in place, rechecking alignment, mark the base locations with a needle point scribe or your preferred method. Then apply an adhesive to the bases and the action, reassemble, recheck alignment after clamping firmly and allow time for adhesive to work. Remove rings and peep sight assembly, carefully transfer punch your receiver thru the base holes, remove the bases, spot, drill and tap each hole from the same setup on the drill press table. When done, your bases will be aligned to the boreline, which is more than you can say for some factory jobs where you don't have enough scope adjustment travel to compensate for mis-aligned holes.
Depth: It is much handier to un-barrel your action for drilling and tapping...but if you want to do it with bbl on don't be afraid to run the tap drill into the barrel threads a little, you will hear and feel the transition, be very cautious, this is where drills are shattered, I prefer to hand rotate the drill the last 50 thou or so.
The most important thing is to calculate the front to rear hole location on the front receiver bridge. Avoid ending up with a hole straddling the locking lug recess and the locking lug abutment. Front hole should be a through hole, rear hole can be a blind hole, you can measure receiver thickness at that point with calipers. If you buy new bases, you can use the screws supplied to calculate depth, remembering to go a little deeper for your bottom tap. I strongly suggest all three taps, start, plug and bottom. Last word, most modern scopes have very short main tubes for the rings on the long '98 action. If you go that route, the front base needs to be an "extension base" or an extension ring, think ahead.
 
The actions are two 95 Chilean mausers and a Carcano. The Carcano is my learning/test action. It will be chambered for a 35 Remington. The Carcano has to be a one piece side mount. One of the mausers is going to be chambered for a 257 Roberts. I have always wanted a 257. Don't know on the other. I have a Swede 96 in 6.5x55 that already had a one piece mount when I bought it. I thought of using one piece mounts on the mausers too because I thought that it would be easier to align to the bore. One piece instead of two. I'll have think more about that.

I never thought of looking through the bore to help with aligning scope mounts. But then again I have never had to align scope mounts before. I'll have to get a long drill. Maybe two. A slightly smaller drill to bore the initial hole and then step up to the finished size. Making the bar is a project I need to do anyway I need a test bar for checking tail stock alignment. It can do double duty by drilling a hole all the way through.

How far away should I put the target? I have a 50 yard range on my property. That's probably too far. I will just have to try some different distances to see what I can see.

Since these are going to be new barrels removing the barrel to drill and tap the holes isn't a problem. That would sure make things simpler.

Thanks for your detailed description on how you do this. Much appreciated.
 
If you have a good size v-block: Drill a piece of round stock with clearance for the stock screws, at the appropriate spacing. Sandwich the v block between this bar, and your action. Put the v block in your vise.
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Mick, Never done a Carcano, Mannlicher style split bridge is a serious challenge. I have done a couple, and found that there are very few true surfaces to work from, everything on the Mannlichers is radiused and contoured. Most of what I posted was applicable to '98 actions, so you will disregard remarks on front hole spacing on your '95's.
When using the optical alignment method of locating holes...I use a very distant object, in my case a white rock about a half mile away. A friend adapted my method by buying a cheap old Bausch & Lomb 4x scope (the oldies with no adjustment ) on Ebay for 25 bucks and uses it with a bore sighting tool (Leupold magnetic?) to eliminate the 1" test bar/peep sight, and gets good results.
When I drilled my 1" bar, I started from each end with a center drill, then went in an inch or two with a spotting drill and then once the 1/4" hole was established just hogged on through with an extended shank hardware store 1/4" drill from both ends. Miraculously, both holes met close enough in the middle that they appeared smooth to the eye. Dumb luck, probably. A pro would shudder at my methods, but my hobbies have necessitated doing the difficult with the tools at hand.
Good luck with your projects.
 
A half mile away. I live on the side of a hill over looking the valley below. I took a look to see what is out there that I could use. There is a white shed about a mile away that I can see through the bore. Lots of other things too that might work.

There is a side mount made for the carcano. The side of the carcano receiver appears to be round. I'll figure it out.

I was going to drill the hole as you described starting with a center drill and then progressing with other drills.

Again thanks for the suggestions.
 
If you’re using a mill, Set the receiver up in your vise. Make a bar to fit the action (I don't recall the exact diameter but seem to remember 14mm diameter). Indicate off that bar to find the center to drill your holes In the action. On the front mount make sure of the location of the hole in relation to the locking lugs as mentioned above. On the front hole you’ll drill down to the threads, it won’t hurt. I usual drill the holes then go back and use the chuck with the tap in it to tap the holes turning the Chuck by hand. You really need a DRO to do it this way. No DRO, drill then tap each hole one at a time.
 
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