Home Forums Hunting & Shooting Gunsmithing 6/48 to 8/40 thread cleanup

Thanks.

Never tried that. Figured it would take some careful attention to detail.

DF

The quick easy fix with a pic rail is to use some new Burris XTR Signature rings. https://www.burrisoptics.com/mounting-systems/rings/xtr-signature-rings

For a more professional fix I would pull the barrel and verify and correct the direction of exit curve in bore. It's a lot more likely the curve is what you are up against. On a custom rifle the curve gets timed straight up and then when you sight in the rifle most of the time the scope only needs a click or two at most from optical center.

When converting an action to 8-40 you should pull the barrel and mount the action in a fixture and then dial in the mill to mill the new holes perfectly straight with the bolt bore raceway using an end mill based on the blueprint rather than the old holes. I personally like to put off enlarging the holes until the 6-48's are no longer feasible. There is virtually no structural strength to be gained with the larger screws due to less threads being utilized. It's about 1 full thread less holding per screw. Running 6-48's is about the same as using 5 screws instead of 4.

I have been through this process several times, not just due to misaligned holes, but wanting the extra ‘beef’ of a 8-40 thread.
The only way to do it correctly is on a mill with the centreline of the action found and to mill the new holes precisely. This is often all you need to clean up the existing hole, if not, then the old holes will need filling, either by a blank threaded plug, or EDM.

I have a Win Model 70 EW with a misaligned hole on the front bridge, you cannot see the misalignment until you place a straight edge over all 4 holes and it is enough to feel the screw drag as you tighten it.
Looks like my next job will be to open those holes up to 8-40 to get things aligned correctly. Well, when I get time...too busy hunting with it.

I returned the DNZ mounts to the manufacturer for them to look over. They said everything was in specs. I will hunt with Iron sights before buying another set of rings from those clowns. Had I not compared the fit with a new set of Talley lightweights it would not have been as bad.