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Lapping bolt lugs

waltermoewaltermoe Member Posts: 958 ✭✭✭✭
edited June 2015 in Ask the Experts
I have been wanting to lap the bolt lugs on this rifle I have, it's a Mauser 98. I have seen where they did it on you tube but it's just the receive their using and the bolt, I don't want to remove the barrel. I figure that I would just put a spent case that I had shot from the rifle in it and work the bolt, but I heard that it better to remove the extractor claw, have the grit worked onto the lugs and then fire a round and work the bolt after firing. Anyone one have any suggestions?


  • tsr1965tsr1965 Member Posts: 8,682 ✭✭
    edited November -1
    If your rifle is a standard hunting/military grade rifle, it has approximately 50% of the surface area between the lugs and action in contact. Most custom rifle builds, have 80 to near 100% in contact. To do this properly, the rifle needs to be headspaced after the lapping is done.

    If it is not to be used for long range precision, it is fine the exact same way it is.

  • navc130navc130 Member Posts: 1,054 ✭✭✭
    edited November -1
    I suggest you read a gunsmithing book on lapping the bolt lugs. The first thing to do is determine IF they need lapping, by applying spotting color to the lugs, work the bolt and see the contact area. Bolt lapping requires pressure against the bolt face.
  • MG1890MG1890 Member Posts: 4,649
    edited November -1
    Respectfully, sir, you are wasting your time. Locking lug contact is only critical on top end precision rifles. On a military action or sporter just consider your forward lug a spare.

    Think of it this way: if you needed contact on the second lug, the first lug would have already displaced until the second lug made contact. So, your first lug is doing all the work, and is strong enough to do so.
  • waltermoewaltermoe Member Posts: 958 ✭✭✭✭
    edited November -1
    I had this rifle built 20 years ago, it is a sporting rifle in 5x57mm, from new bolt handle to trigger to stock I have had about all you can do to it, done. A lot of the work I done my self under the careful eye of a gunsmith that was well known in are area and who I would say was always willing to share his skills with some one if they wanted to try there hand. The only problem I have ever had with the rifle is that, when trying to open the bolt after firing, it is a little tuff rotating the bolt, I told this gunsmith about it 3 or 4 years after I had it and he told me the lugs needed lapping. Well he has passed on now and I'm just now getting around to doing it. Rather than just pulling back on the bolt and working it, I thought that maybe it would help hold pressure on the bolt while I worked it if I left a fired case in the chamber.
  • asphalt cowboyasphalt cowboy Member Posts: 8,875 ✭✭✭✭
    edited November -1
    While there are a few exceptions, a fired case isn't going to exert any pressure to the bolt face. Even in those few instances it's not going to exert the constant pressure needed for lug lapping.

    Is it stiff only after firing, or also when cocking the rifle with an empty chamber?
  • charliemeyer007charliemeyer007 Member Posts: 7,345 ✭✭✭
    edited November -1
    Maybe some JB Bore Paste applied to the lugs with a q-tip. You could rig up a special case that had a drilled out primer pocket, with a fitted rod and spring inside so that the rod would push against the bolt face. I don't think you could polish off enough to change the headspace enough to worry about.

    Is it a 6.5mm?

    Added: you are welcome, lets us know how it works out.
  • waltermoewaltermoe Member Posts: 958 ✭✭✭✭
    edited November -1
    It is only stiff after firing. It is a 7x57mm, and you gave me an idea with drilling out the primer pocket and using a spring and plunger, that might just be the solution, wouldn't be that hard to make.
  • jonkjonk Member Posts: 10,121
    edited November -1
    If it's just a military barrel and action I agree, it isn't worth it. With a good handload it's never going to be more than a 2-1.5 MOA gun, especially with stock sights.

    If you plan on fitting a new target barrel and scope or target sights, it may well be worth it, in which case taking to a smith is well worth it.

    Now, if you want to try it, "Just because" after coloring the lugs to determine high spots, I'd go with progressively finer grinding compounds with a good cleaning in between.

    As for headspacing, if you still are using the military barrel, a few thousandths off the receiver locking face or bolt lug face or both won't make much of a difference. Even if it did, you can always fireform brass and neck size only.

    If you're after accuracy, I'd suggest checking metal to wood contact first and working up a good handload before I played with the locking lugs and lapping.

    Edit: I had missed your response about it being a sporting rifle.

    You mention the bolt is a little hard lifting. That could mean lug setback. A simple way to check that is to take the spring out of the bolt and close it, then see if it moves back and forth any while locked.

    Lug setback, if minor, isn't the end of the world by any means; but it is something to be aware of. If it's just a few thousandths of an inch than lapping may help a bit, but if more than that, you're just chasing something that isn't going to work.
  • waltermoewaltermoe Member Posts: 958 ✭✭✭✭
    edited November -1
    Hello Charliemeyer, I took your idea an ran with it. I took apart and old 20ga. snap cap, it had a quarter inch brass rod that that had a 23-64th ring to hold the spring, it is all one sold bar, I then drill out the primer pocket 23-64th, the spring and plunger fit perfect, I then used a Sierra 100gr hollow point bullet and seated it backwards until flush with the neck, the spring goes in the rear and then the plunger, I then adjusted the bullet until the plunger sticks out a quarter of a inch. I'm not sure how much press there is when the plunger is pushed in, I'm going to say maybe 15 or 20 pounds so it should hold a good constant pressure on the bolt. THANK YOU for the idea.
  • Okie743Okie743 Member Posts: 2,241 ✭✭✭
    edited November -1
    I use a permanent marks a lot pen usually black as a spotting color on bolt lugs and also for others such as when sharpening large drill bits so as to see when both sides are equal ground, etc.

    I also sometimes use a bic cigarette lighter turned up to high flame and play the part across the tip of the flame rapidly so as to smoke (smut) the part to see a fit pattern impression. It's easy and fast and the smut wipes off easily.
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