Lapping lugs

[Jdaniel343]

I have a Winchester HBV in 220Swift. It shoots 3 shot @ 0.25, 4 @ 0.50 and 5 @ 0.75.
The first 3 are basically 1 hole. I am not sure why the flyers. These groups were fire in no wind, 50 deg at 100yds.
Rifle is heavy barrel, HS stock with alum bedding block, action screws at 65 in lbs, scope bases 35 in lbs, rings at 35 in lbs. I'm using a front BR rest with rear rabbit ear bag.
Brass has been prepped. Gun use to shoot 5 shots @ 0.35 consistantly.
I am not sure what is going on.
I've been looking at the action and notice last night that only one bolt lug is making contact (100%), the other doesn't appear to be touching at all (may be 2%).
I was wondering if I will hurt anything by lapping only the lug that is touching now until the other comes into about 70%. Will I hurt the 100% lug?

Thanks

 

[spclark]

I have a Winchester HBV in 220Swift. It shoots 3 shot @ 0.25, 4 @ 0.50 and 5 @ 0.75.
The first 3 are basically 1 hole. I am not sure why the flyers.

This allowing for your barrel to cool down between shots? Which direction are the flyers opening up your groups? If vertical it's likely a warming barrel, if horizontal it could be that slacker lug....

I've been looking at the action and notice last night that only one bolt lug is making contact (100%), the other doesn't appear to be touching at all (may be 2%).
I was wondering if I will hurt anything by lapping only the lug that is touching now until the other comes into about 70%. Will I hurt the 100% lug?

Hurt it? No, but understand you'll be taking metal off it until the 2% lug is where you want it to end up. Lug lapping is done so that the lugs bear equally - as much as is practical - when locked up.

 

[Larryh128]

1st run some lay out dye on the lugs (or red nail polish) & work them back & forth & then check them for contact. USUALLY, a 1 lug contact rifle wouldn't shoot at all. You won't hurt anything by lapping the lugs because you will be lapping both, not just the one not hitting properly. The only thing that you are changing is adding a slight growth to the headspace. However, to do a really good job of lapping, the barrel needs to be off & pressure exerted onto the face of the bolt while you are working the lugs back & forth with compound on them.

 

[Jdaniel343]

Yes the flyers happen to be horizontal.
While lapping the lugs I just want to make sure I am not hurting the bolt. Yes I did apply layout fluid to the lugs, that is how I determined that only one lug is making contact.
It just seems like I'll be taking quite a bit of material off the lug that is making contact before the other lug even shows it starting to make contact.
Should I be concerned?

 

[spclark]

It just seems like I'll be taking quite a bit of material off the lug that is making contact before the other lug even shows it starting to make contact.
Should I be concerned?

Depends.... Like Larryh128 described, there's a little more to lapping lugs than just putting compound on them then working the bolt.

If you have any doubts about your ability to perform the operation to your satisfaction, you might want to look into having a professional gunsmith "true up" your action, at least as far as the bolt lugs are concerned.

Once the lugs are lapped in & making good contact, the bolt face might then benefit from "squaring up" too. If you feel that so much metal needs to come off the lug making good contact now, once that's resolved your bolt face may no longer be square to the bore axis.

 

[Larryh128]

GENERALLY, you are not going to remove more than .002 of material. This amount would not normally create excess headspace unless you are on the deep side already. .002 wouldn't be dangerous to fire but could cause shortened life on your brass. What I would think about doing 1st is having the bolt lugs squared on a lathe. A LOT of times you're only talking a couple tenths to bring them in. The worst that I've ever seen was .002 on 1 lug. IF the lugs are squared, there is a good chance that will cure your problem. I've seen several rifles go from OK to WOW by squaring bolt lugs & it's easier & cheaper. The very 1st thing that I do to a new reciever is square the bolt lugs, unless you have a custom action,they all need it.

 

[spclark]

IF the lugs are squared, there is a good chance that will cure your problem.

What of the lug mating surfaces if the action's where the problem is, or both?

 

[Larryh128]

That's a definite maybe. Both could be off BUT if the bolt is set up on centers on a lathe & one lug is short, that is definitely a problem & needs to be addressed first. A lot of times, squaring the lugs make the problem go away without removing the barrel etc. It's really the proper place to start. IF they both indicate in OK than you know the problem is in the reciever. I did 2 last winter that had accuaracy issues & they were both related to uneven lugs. The one turned into an absolute 1 bug hole rifle.

 

[Jdaniel343]

Thanks for the info.
I'll set up the bolt in the lathe and check the lug surfaces.