Bolt lug lapping

6mm Shooter

6mm Shooter

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Has anyone ever lapped their own bolt lugs? Where did you get the silicone carbide lapping compound? What grit did you start and end with? Did you use a tool to keep pressure on the bolt or did you just keep thumb pressure on it? My Stealth bolt barely touches on one of the lugs. I think it maybe the cause of the poor accuracy.
 
I use 120 grit I bought from Brownell's Inc. You can use automotive valve lapping compound. The bolt should be stripped and something used to push the bolt straight back while you lap. Then it must be cleaned very well so no grit remains. Lapping a bolt removes so little material headspace does not change hardly enough to measure. Don't worry about that.

I doubt your accuracy problem has to do with one lug touching more lightly than the other. In an extremely accurate benchrest rifle you may see a difference, but in a factory rifle such as yours probably not. What is the rifle chambered for? What is the quality of the brass?. Etc, Etc, Etc. A lot of factors in accuracy.
 
Lapping is going to affect headspace. If headspace is changed enough, it could be necessary to set the barrel back to correct for excess headspace. Here is the procedure which I have used to lap lugs, in a nutshell. Remove barrel. Use iron lapping tool running on mandrel through boltway to true up locking seats in receiver. Strip bolt. Apply lapping compound to rear of bolt lugs, gently install bolt. Screw tool into front of receiver to apply pressure directly to the face of the bolt. Raise and lower bolt handle while maintaining pressure on bolt face, using the tool. Clean and repeat as necessary. Clean all traces of lapping compound. While barrel is off, might as well set the receiver up on a mandrel between lathe centres, and true the face of the receiver. Reinstall barrel, adjust headspace as necessary. I use 600 grit compound, which I purchased from Brownells. You want to use a non-embedding compound.
 
I agree that lapping will affect headspace but I have never seen it change more than two thousands of an inch and that was an extreme case.... usually about a thou.

But if you have the ability to remove the barrel and (Use iron lapping tool running on mandrel through boltway to true up locking seats in receiver. Strip bolt. Apply lapping compound to rear of bolt lugs, gently install bolt. Screw tool into front of receiver to apply pressure directly to the face of the bolt. Raise and lower bolt handle while maintaining pressure on bolt face, using the tool. Clean and repeat as necessary. Clean all traces of lapping compound. While barrel is off, might as well set the receiver up on a mandrel between lathe centres, and true the face of the receiver. Reinstall barrel, adjust headspace as necessary), you wouldn't be asking about lapping lugs. :D
 
It is a 308 stealth and with 150gr sp winchesters the best groups I can get are around 11/2 inches. One other thing I have noticed is that the firing pin does not hit in the centre of the primer. I will be loading the win brass with 168 hpbtmatch Hornady bullets and 45 - 46gr of varget to see if I have better results.
 
I would agree that headspace increases as one laps locking lugs. How much of a concern increased headspace is I guess depends on the shooter and how sloppy the headspace was in the first place. I've always felt that tight headspace, as long as not too tight to interfer with proper function, was best. I don't agree that valve grinding compound is a good material for this job. I've found it is far too agressive for most gunsmithing. Better to use a finer grit material and more elbow grease. Way too easy to over do it with anything too course.
 
Ideally, the bolt should be pressed straight back against the locking seats while being lapped. The method I described is more appropriate if a new barrel is being installed. Without a way of applying a load to the face of the bolt, rearward pressure will be applied either by hand on the bolt handle, or by the cocking mechanism if the bolt is not stripped. Either of these may result in a twisting or lateral load. In practice, whether this would be detrimental is open to question. Carefully done, the lug which is engaging could be reduced somewhat, and the other one brought into contact. A couple of thousandths increase in headspace isn't going to create an unsafe situation, and if you handload, is irrelevant. Careful handloading might result in better accuracy, all by itself. Something that factories rarely mention is the standard of accuracy of which their rifles are capable. It could be that 1 1/2 moa groups with factory ammunition are within acceptable limits.
 
Thanks for your thoughts guys. I am uncertain what to do at this point. I could take it back to the gun shop but I got a good deal on it. So is it worth the work to get it shooting? I bought this gun mainly for punching paper and shooting gongs out to 600 yards. It was getting expensive shooting the 300 win mag. Anyone know what it would cost to take the barrel off and get the action and barrel face trued?
 
6mm Shooter said:
Thanks for your thoughts guys. I am uncertain what to do at this point. I could take it back to the gun shop but I got a good deal on it. So is it worth the work to get it shooting? I bought this gun mainly for punching paper and shooting gongs out to 600 yards. It was getting expensive shooting the 300 win mag. Anyone know what it would cost to take the barrel off and get the action and barrel face trued?
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I thought valve grinding compound came in different grits. If it does use nothing coarser than 120 grit.

I have found 600 grit to be extremely fine and my experience lapping with it is like polishing more than lapping. It takes a lot of lapping with 600 grit to get results. You can try a test using 600 grit wet or dry sand paper and a piece of steel. Try sanding the steel with the 600 grit and you will see how fine it is. Then try it with 120 grit wet or dry paper. It too is quite fine but it cuts a lot better.

Properly bedding the action may help some. (All types of stocks can benefit from a good glass bedding job). Working the load some more using only match bullets may get the groups down. Make sure you clean all the copper out and see which groups better, a clean or slightly fouled barrel. Make sure your scope mounts are solid. Is the scope good?

The off center firing pin is not easily corrected although I am not sure how much that is affecting accuracy, it can cause a misfiring problem sometimes.

Trueing the action all up may not help either if the problem is within the barrel. Some shoot better than others....... it is a possibility that it may not shoot much better.
 
Before you get carried away with lapping, trueing, etc, you might want to try the bedding route and ammo--one of your posts said you were using Win 150 gr sp ammo--you should perhaps try some match ammo or load up some test ammo tailored to your rifle.

44Bore
 
I loaded up some 168gr hpbt match Hornadays in front of 44.5gr - 46gr of varget with fed 210 primers last night and shot them. The cases were trimmed to 2.008 inches and the bullets were seated .0010 off the lands. To say the least I was not impressed. My best 5 shot group was 1.25 inches and the average was still around 1.5 inches. I don't know, I want better and now that I know the bolt lugs are not mating properly it is stuck in my head. Things are not square. The face of the left side of the bolt has the blueing worn off and the right lug shows alot of wear on the locking surface. I don't think I will have faith in this rifle until I have it trued.
 
6mm Shooter said:
I don't think I will have faith in this rifle until I have it trued.
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In that case have it done ,or no matter what you try you will always be wonderingif things couldn't get better and end up spending too much time thinkin and out-thinking yourself
 
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