I own a Ruger KVT M77 in .308 and the bolt lugs don't seem to be making full contact when closed.
Which device would you used to lap the lugs without removing the barrel, and would the headspace need to be reset afterwards. Thanks for the help.

Welcome to the forum, teele1

I had a rifle that had only one lug making contact. I used black permanent marker as lay-out dye and the spring pressure of the firing pin to lap, no extra used, except I put a cleaning rod in the bore, let stand vertically as I lap, to add pressure. There's very little metal removed, I didn't set back the barrel shoulder and had no trouble.

Be careful not to lap the sloped camming surface, you want to lap the flat area of the lug only, bolt lift should not be full. Remember to get all the abraisives out.

Tell me more about the lug lapping process, if you don't mind.

What lapping compound do you recommend? Do you do this with various grits; heavy grit initially and fine grit to polish?

If I understand the process, you are putting a small amount of compound on the inside of the action on the flat surface associated with the contacting lug only. Then you just keep lifting/lowering the bolt slightly to wear down one of the surfaces reapplying compound as needed to continue cutting. The range of movement should correspond to the flat area (non-camming)inside the receiver. You do this until the non-touching lug makes contact.

Do you continue to lap both lugs a small amount to ensure better contact?

I'm not concerned about headspace changes as the gun will be getting a new barrel very shortly

Thanks,
Ron

Reposted by request---

The process should be to apply an even pressure against the face of the bolt in line with the bore while rotating the bolt. This is usually done by a dowel that runs through an old section of barrel and pressure applied by hand or a compression spring if you get fancy.

Lapping lugs does two things; First it makes more steel to steel contact for better transfer of energy from the bolt to receiver. It makes racing slicks out of street tires. It also cuts away the little ripple that forms as the metal flows from pressure. Mausers will have one where the split lug seats, too. When working on Mausers we can assume the action has been fired several if not many, times. The result of this firing is a very slight "dishing" of the locking lug recesses where the lugs bear against it during firing. When more than a couple thousandths its called "set-back". It’s where headspace comes from.

The problem is that by “reading” contact on the lugs by looking at the lugs doesn’t work. That pattern on the lugs is a “wipe” pattern, not a contact indicator. Only if there is a smoothly lapped surface inside the receiver does it mean there is good contact.

Anytime I see opposing corners contact I think the bolt is crooked in the action. That can be caused by pulling on the bolt handle as its lapped. All the pressure should be from straight ahead. You need a guide for that. Old military barrels make excellent guides.

Jack been trying to contact you, is the computer still crashed?

Wondering if you shipped the rifle.

FlyDevil,

Your perception of the process is correct. You can use different grits if you want, but I doubt there's much need for that. You can buy abrasives in bags or you can burn a piece of sandpaper and collect the ash if you don't see the need for a large amount.

Pyrotek,
Thanks for the response. Like that idea of burning sandpaper. Never heard of it before but "pyroteking" (pun intended) sounds clever.
Ron

FlyDevil - valve grinding compound is what is most commonly used. Headspace should most certainly be checked as it can be affected. I would really recommend that this be left to a professional.