Only one lug is making contact in my Weatherby Vangard. Can I use the lapping compound that comes with a NECO fire lapping kit. The only stuff I can find localy is the valve grinding kind and I think it is a little too course.

Clover brand lapping compound comes in various grit sizes. Coarse thru fine. MSC sells all 3.

Do you have a go/nogo gage ? I think you better leave lapping to the people who know how , or send it back to Weatherby with a letter to correct the lug to action fitting , or you may be wearing part of that bolt in your forehead !

Hart:

Dependent on how far out your lugs are you may find it quicker to set the bolt up in a lathe jig and turn off about .001 too .oo3 then lap the lugs. You will have to set the barrel back and rehead space. This is a must! If you have only one lug touching it could be unsafe and definately will torque your action when it is fires.
Longshot

The target that came with the rifle (338) had a 1" three shot group. I thought that after working up some hand loads I might be able to improve on that group. Unfortunatly my groups were almost double that. I did not do a lot of load work since I could see the blue had worn off of one locking lug and the other looks untouched and figured that it was pointless to do more shooting till I get this problem fixed.

That is why I was asking about using the abrasives in the NECO kit, since that is what I have on hand and is in four different grades. I think the abrasive is silicon carbide but just want to make sure. The Brownells catalog says silicon carbide is the best compound for "hard fitting" two pieces of steel.

I myself will be truing and then lapping the lugs on a Sako today. The bolt lugs are off by a little over .002. Of course I will be setting the barrel back in the process to close the throat and to machine an improved chamber, so the headspace increase from truing the lugs won't be an issue.

Lapping should never be used as a substitue for machining when closing distances. Lapping is used to apply a finish, or, improve the fit between 2 mating surfaces.

If there is absolutely no contact with one of the bolt lugs, as is the case with the above Sako, then mere lapping in an attempt to obtain contact is not the way to go. The amount needed to obtain the correct degree of contact will likely require a headspace correction.

Save the lapping for those conditions where the lockup is rough, or, where there is some amount of engagement visible on both lugs.

Since it takes so little to go from "go" to "no go", I would highly recommend that before you commence any lapping, that you first determine the exact headspace measurement, and check it frequently as you go.

Unless you have a set of adjustable or "incremental" headspace gauges, you will need to pull the barrel to get the measurement. That is why it is recommended that a gunsmith do this work. They are usually better equipped to do it.

Just a bit of advice before you start chucking your bolt into the lathe. Have you checked the receiver threads and the receiver lugs for squareness to the bolt raceway? At this point, for all you know, it just might be the receiver lugs that aren’t square and even and that won’t be cured by just doing the bolt lugs on a lathe.

quote:

Originally posted by Rick 0311:
Just a bit of advice before you start chucking your bolt into the lathe. Have you checked the receiver threads and the receiver lugs for squareness to the bolt raceway? At this point, for all you know, it just might be the receiver lugs that aren’t square and even and that won’t be cured by just doing the bolt lugs on a lathe.

Absolutely! If you're going to have to machine ANY part of the action, you had better have a good, square point of reference from which to obtain your measurements.

If however you have a bolt lug that isn't making contact as in the case of my customer's Sako, a quick measurement of the bolt lugs can be obtained by dialing in the bolt body in the lathe, and then measuring the position of each lug. If the lugs are not square or uniform, now would be a good time to true them up.

This will more than likely require a headspace correction. So when you pull the barrel to make the necessary correction, NOW would be the time to check and true the receiver as Rick has mentioned.

Whatever you do, don't be tempted to make one correction, if you're not equipped or otherwise able to make the other corrections.

Think brake job.

Would you change the pads/shoes without checking the disks/drums and the cylinders?