Gunsmithing Crooked rail threads on a Remmy

[Daneren]

Hi,

A good friend of mine, only has about 1.5 MIL of horisontal movement, to one side. The scope is an K624i in good condition, and on his other rifle, the movement is symmetrical.
I'm thinking the threads for the rail might be off center, but I'm unsure. I haven't seen the rifle myself yet.

Is this a common problem with LA Rem 700 actions?

How would you go about fixing this issue?


The action is in stock configuration (not blueprinted).


My idea is to mill out the old threads, and tap/mill some new, on my 5 axis cnc mill. But I'm unsure of what to indicate off of. As my understanding is, that Remingtons barrel threads are anything but true to the actions centerline. I have a rather well equipped machineshop at my disposal, but I do not have rangerods.
Which threads would be the top choice for the repair? If crooked threads is the problem, that is.

Thanks in advance.

 

[Gene Poole]

It may just as well be the crooked threads you mention with relatively straight scope base screws.. That's why most "blueprinting" jobs include not only aligning the tenon threads to the bore centerline, but also punching out the scope base threads from 6-48 to 8-40. A 9/64 carbide 4-flute end-mill will punch the holes out to the correct diameter for an 8-40 tap. Use the same tool you use to align the threads and lugs to the raceway. Something like this:

http://pacifictoolandgauge.com/mandr...ruing-bar.html

And you'll need a set of these too:

http://pacifictoolandgauge.com/161-action-blueprinting-bushings-nopix-

 

[Threadcutter308]

I would chuck up the receiver in a mill vise, get it aligned on the bed via dial indicator on the action mandrel, then run the dial indicator down the side of the affixed scope rail. That will show you whether the rail is crooked or not. If it is crooked, you will want to measure how far the front portion of the rail is out, then move over in the opposite direction by the same amount for your new hole. Repeat the same measurement and adjustment for all holes. Either the back or the front hole will remain in the same location (unless you're a masochist.....). The new holes are going to overlap the old ones, so going to 8-40 does a nice job of compensating for that. Instead of the front hole, you may have to do it on the rear if the geometry of the receiver and the bottom of the rail requires it.

Edit; Chad's usual excellent advice below made me realize I missed saying something that is important here. Once the center of the action/proper hole location is determined, the re-located holes would have to be re-drilled with an end mill, not a standard twist drill. Chad is exactly right, re-drilling (with a standard twist drill) the existing holes for a bigger screw does nothing to correct the mis-alignment. Chad is in the enviable position of having a 5 axis crunchenticker CNC, but for the rest of us neer-do-wells, an end mill on a 3 axis mill will have to do.

You might want to install the rail, scope rings and a lapping bar in the rings (temporarily) and measure down the side of the lapping bar. This, after aligning the receiver in the manner described above. Granted, the lapping bar isn't ground and it probably has a thou or two of runout, but with what you have described, you (potentially) have much bigger tolerance problems than that.

BTW, have you tried to optically center the scope ? It might simply be a scope problem. I'm thinking there are some good instructions from some really smart people over on the Scope forum. Check out the stickies....

 

[LRI]

Best way I've found to resolve an action with optic holes out of position:

:52 second mark illustrates this. Drills and taps don't fix this. They just make the problem bigger. The bore must be bored. If traces of the original hole remain the threads need to be single point machined in order to maintain position.

https://www.youtube.com/watch?v=wNy7SSYHWsc

 

[Daneren]

Thanks for the advices guys.

I got the action last night, and just by looking down the action, I can see the threads are misaligned.

I'll mill a fixture for the action. Make a couple of bushings to accept a ground carbide rod, to indicate off of. Holes will be ramped out.
The machine is a brand new 5 axis Hermle C42u. I've got the proper tools, don't worry ;-)

I'll keep you updated.

 

[Daneren]

I promised a followup.

Finally had some time to spare, so I finished the job on the Remmy.

I've never doubted that Remington was kinda "meh" in their quality, but this action takes the cake. I'm never touching one again

It turned out well.

Thanks for the help.

 

[LRI]

I would certainly say that you have the correct tools. Very nice. Smart not to bias the action in a collet as well.

Handled! lol.