Gunsmithing R700: What's the best way to align a scope base to the bore?

[Gene Poole]

I'm fixing to do a receiver truing job on a R700 and I'd like to overbore the scope base screw holes to 8-40 and ensure alignment with the bore. How is this typically done? Should I make a barrel stub? Will running an edge finder on the truing jig (I've got the Manson setup with the 0.700-0.705 conical bushings) be sufficient? I suppose that once the truing is done, I can assume that the raceway will be aligned to the bore, but that doesn't ensure the receiver OD is aligned to anything. I'll have to shim the action or adjust the mill vise to align the jig to the mill axes and that'll certainly take a lot longer than it did in the lathe. There's got to be a simpler way that I'm failing to discover.

 

[JJones75]

Assuming that you will true the receiver to the bolt race way you could use a mandrel to get the receiver strait.
Get a V bock that you can screw the action down in and hold it in the vice then put the mandrel in the action and an indicator in the spindle and adjust so that its running strait.
Use an edge finder to get your take off of the mandrel and find center of the action.
The trick is gonna be finding an end mill to cut the hole wit because a drill bit will follow the existing hole.

 

[FCrifles]

9/64 endmill will have you in business.

 

[FCrifles]

9/64 end mill will have you in business

 

[STR]

I'm just curious, how far off do you think the factory drilled holes are? How are you going to line them up with your now trued bore without oblonging the factory drilled holes? I've never had to do that, so that's why I ask. The scope has always had pleanty of side adjustment to correct for any minor misalignment. The new holes are not that much bigger than the smaller 6-48 holes are. If you do it, I would like to see what it looks like. Always looking to learn. Thanks

 

[hero's machine]

touch off the truing mandrel in a couple spots and check the current holes......easy to check and might save you the work.

 

[JJones75]

I'm just curious, how far off do you think the factory drilled holes are? How are you going to line them up with your now trued bore without oblonging the factory drilled holes? I've never had to do that, so that's why I ask. The scope has always had pleanty of side adjustment to correct for any minor misalignment. The new holes are not that much bigger than the smaller 6-48 holes are. If you do it, I would like to see what it looks like. Always looking to learn. Thanks

I always use to do this "just because" and have realized that its one of those things that their is little to no benefit especially compared to the time involved. I have often thought "if you bang your scope hard enough to shear off the 6-48 screw then the scope is likely destroyed.
I can see it being a worthy venture if the holes are buggered up or badly out of line but for a strength stand point I believe you would be far better off puting a dowel pin in the action and base.

 

[Gene Poole]

I suppose I'll check out the alignment first; if it's good, then I may just leave it. I still need to know how to do that, hence my original question.

I had a factory R700 that was apparently mis-aligned: when dialed in at 100, you'd need an extra 0.1 mil of right windage per 200 yards. At 600 yard F-class matches, I'd have to dial in 0.3 right windage before taking my sighters. Chad Dixon trued up and rebarreled that action (including redrilling the base holes) and it was dead-nuts at all ranges after that.

 

[Killswitch Engage]

I've never shot it no wind condition to know that .1 wind
at 200 wasn't real wind or a mechanical condition. Was there any barrel curvature? How about the rail, was it dead nuts to spec and alignment? .1 at 200 is pretty minute and would seem hard to discern.

to check alignment couldn't you just indicate the mandrel to zero run out and then touch off your indicator at each bolt hole? I would think installing the screws might even make it easier to get a reference off of the heads. You could also install the base and run your indicator along it to see if its true.