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Old November 2, 2010, 02:28 PM   #1
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Bolt lug lapping and headspace

Will lapping the bolt lugs on a bolt action rifle increase the headspace to a dangerous point if the same barrel is reinstalled? How much material is actually removed by lapping the lugs?
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Old November 2, 2010, 03:23 PM   #2
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It depends on how uneven the bolt lugs are. It's certainly possible to have to remove enough material to affect headspace.
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Old November 2, 2010, 07:25 PM   #3
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It's also very possible to lap right through the case hardening on Mauser rifles if you lap too much.

Best answer is, it depends on the individual rifle and how much lapping is needed.
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Old November 2, 2010, 09:29 PM   #4
James K
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At the extreme, I once saw a rifle that had been rebarrelled by a "gunsmith" using a take-off barrel. He ended up with a very short chamber and apparently didn't know about reamers. So he ground about 1/8 inch off the rear of the locking lugs. The customer couldn't get the gun to fire (he was lucky) and brought it to us. Had it fired, the result would have been disaster, as the whole back end of the round was totally unsupported. Yet, the rifle headspaced properly by the gauges!

Jim K
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Old November 2, 2010, 10:30 PM   #5
Edward Horton
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On new .303 British Lee Enfields an oiled proof pressure cartridge was used to seat the lugs and bolt head. After setting the headspace as close as possible to .064 the rifle was proof tested, the Enfield was then checked with a .067 head space gauge and if the bolt closed on this gauge the rifle failed proofing due to excessive lug setback.

An oiled proof cartridge seated the lugs to the receiver and this is why your chamber should be kept oil and grease free because oil doubles the bolt thrust and can damage your rifle.

Also on the No.4 Enfield the replaceable bolt heads only went to a number 3, the reason for this was simple, it was found that by the time a number 4 bolt head was needed the receiver lug recesses had worn through the case hardening and the rifle was sent for overhaul.

Did you ever wonder why Savage-Stevens rifles have a bolt head the pivots on the bolt?
(when the bolt is closed "both lugs bear evenly)

Eat your heart out..................and why lap your lugs when you can stone the bolt lug to fit???
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Old November 3, 2010, 02:11 AM   #6
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Typically the locking surface of both lugs is cut in the same setup,same cut.I have seen surprizingly poor tool finish on the rear of a bolt face.
same inside the receiver,both surfaces were made with the same cut.So,maybe we get a little heat treat distortion.
I think maybe where a lot of folks get fooled is inking the lugs and grabbing the bolt handle.Grabbing the bolt handle and working it tips the bolt wthin its running clearance.The lug on the bolt handle side will bear heavy.
The pressure really needs to be applied to the bolt face,and the handle used for rotational force only.
I also agree,if you have a high lug,carefully stone it a little at a time til you have some contact on both lugs.Then I lap to up the percentage of bearing.
This all shouldn't be about more than +-ballpark .001 or so,maybe .002This should not be a heavy handed thing.Unless headspace is already borderline,not to worry.There are the go/no go gages for chambering,but it is the field gage that says its too much.
I'd rather have a rifle bearing on the lugs and a bit loose in headspace than a tight headspace with poor bearing.
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Old November 3, 2010, 11:04 PM   #7
James K
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Edward Horton wrote: "Did you ever wonder why Savage-Stevens rifles have a bolt head the pivots on the bolt? (when the bolt is closed both lugs bear evenly)"

Well, no. The locking lugs (the front set) don't pivot on the bolt and there is no special way to ensure they bear evenly. The rear set do pivot but they are not locking lugs. They simply seal the bolt raceway against possible gas escape; they don't bear on the receiver.

Jim K
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Old November 3, 2010, 11:11 PM   #8
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aqccording to Savage the "floating bolt head" elimiates the need for lapping
and assits(they say) in keeping proper headspace. Mine have had 100% bearing without stoning or lapping
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Old November 4, 2010, 09:20 AM   #9
F. Guffey
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There was a time when blue lay-out fluid was used, not necessarily to find out if both lugs were engaging but to fine the percentage of engagement or contact, 75% was good. Bolts with far less contact were were expected to improve but the belief was as the bolt contact improved the bolt would set back, causing an increase in head space. I have a Pratt and Whitney gage that measured beyond .0000, made by GE, I had no use for it in that configuration so I removed the electronic gage and installed a dial indicator, with a height of 11' it works better as a height gage when adjusted with standards, point being? The electronic gage would measure the finish and surface height, with any other gage the surface measured .000, with the P&W gage the surface looked as though it was rough cut.

For those that measure before and after, the amount of bolt set back can be determined, for those that can measure the effect a bolt has on head space can determine the amount of material material necessary to to get both lugs to make contact.

And If I need a bolt that increases or decreases head space there are two people I can call, the rest suggest trial and error.

F. Guffey
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Old November 4, 2010, 09:29 AM   #10
F. Guffey
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of material removal necessary to allow both lugs to make contact.

Sorry about that,

F. Guffey
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