Misaligned Scope Mount Holes

[Harrisbg]

I have a BSA sporterized Model of 1917 that I am building into a 6.5-06 A.I.. After removing the .30-06 barrel, I used a scope mount drilling jig to check the holes that were already drilled in the front and rear of the receiver, and found that the holes are drilled off center. What are my options for repairing the holes, and having them re-drilled correctly?

 

-Byron

[724wd]

any chance you can drill them oversize, like 8x40 or 10x40? (assuming the holes you have now are 6x48...)

[Spiris]

Is there any way to offset the drill jig, front to back, to miss the old holes? How much off are we talking here?

I've heard that some epoxy heat softened screws into the holes and clip them close and file down after allowing proper dry time. Then D&T.

I've also heard that a quick tig weld of screws in the holes will do it, but I would be concerned about any damage to the heat treat in the front ring. Perhaps someone with more expertise can advise.

 

 

Spiris

[Limpid Lizard]

Your post leaves more questions than whether you can do anything to straighten the holes. First, was the rear bridge ground correctly? Can you obtain bases if you do straighten the holes?

 

If the holes are drilled off center, and the bridge is not ground to accept commercially made bases, your best bet would be to make bases to fit the holes and the bridge.

 

If you can get a base that fits, and you open the receiver holes to straighten them, you will also have to recountersink the holes in the bases.

 

In addition to checking to see if the holes are off center, you need to ascertain whether the holes are straight. If they are #6 screw holes, an endmill is the best way to straighten and enlarge them. Off the top of my head, I am thinking 3/16", but you had better check. An 1/4" endmill properly centered over the existing base counter sink hole will open the hole to accept a #8 screw head. If you are using weaver style bases, you will need to change to flat bottomed screw heads.

[Harrisbg]

When I took the scope off that was on it, I noticed when I shouldered the rifle that the flats on the top of the bases weren't aligned to each other. Whoever had installed the scope just cranked the mounts down and pulled the scope into place. The scope was a 1970's era Redfield 3x9. I believe one mount was a 46S, and the other was a 45S. I'm not working at home, so I don't have them in front of me now. The rear mount has a very close asymmetrical screw hole spacing, with one screw through the cross slot, while the front mount has evenly spaced screw holes on either side of the cross slot. There were no shims under either mount.

 

I'm making an assumption that when BSA sporterized these actions that they ground the rear receiver correctly. The rear bridge is where the BSA logo was placed (BSA inside a wreath, not the stacked rifles), over the tightly filled oval slot. The work is good looking. You can only see the plug because it blued to a dark blue-black, while the receiver is kind of purple blue, like an old Ruger Security-Six. If the rear bridge is correct, the front mount is slightly rotated to the left, looking from the rear. I leveled the receiver in a machine vise, and the used the flat bottom of the receiver as a reference point. I then placed small Starrett levels across the mounts. The rear mount level's bubble was in the middle, while the front mount level's bubble was off to the right, leading me to think the front mount is rotated to the left.

 

I then installed the scope mounting screw jig. It's the type that has two thick plates along the bottom of the receiver, a machined rod that goes down the center of the action that has two stand-off bushings, and a top plate that fits to the stand-offs. This has drill bushings where the holes are to be drilled. Two long 1/4" bolts go through from top to bottom that when tightened up bring the rod to the apparent center of the action, and tighten the whole thing in place. When looking down through the holes the drill bit bushings go through, the existing holes are not centered, but 3 of 4 holes are 1/2 a #6 screw hole diameter off in different directions, both front-to-back, and side-to-side.

 

I would like to fill the holes, and re-drill them correctly if possible. This is my first project that wasn't a straight barrel swap on a Remington 700, or re-barreling a Garand. Is tig welding the screw holes the only option I have? I bought this rifle for this project because it already had some of the work done, but it's not working out with the scope mounts.

 

-Byron

[sonic1]

this is a option i"ve used..http://www.midwayusa.com/viewProduct/?productNumber=712472

 

just depends on what you are wanting to do...get the mounts to line up...or just get the scope to lineup

[riceone]

If it were me I would use loc tite and screw existing screws in tight as I could. Let set and then file the head down leaving about a finger nail thicknes of the screw. Use a small hammer and flatten whats left of the screw, then file and sand smooth and re-tap. riceone

[Harrisbg]

That may be what I'm going to do. Someone has already filled at least one hole on the rear bridge like that. That has the difference in bluing. I have another rifle that has the oval plug. Here are some pictures.