Lapping bolt lugs

stangfish

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Joined
Dec 31, 2008
Messages
224
I was curious what grit you guys use for lapping the lugs. I had some 2-4 micron diamond lapping compound from a job I did and used that. It lapped the lugs in fine but it put a mirror finish on the abutments and lugs so now it squeaks when you operate it without lube. What grit or micron do you use? Thanks in advance.

Stangfish
 

bpctcb

Member
Joined
Jan 30, 2011
Messages
5
The grit I start lapping with depends on how bad the lug contact is to start with. I may have to start with 120 sometimes. Usually finish up with 320 or 400 IIRC. I have a abrasive lapping kit from Brownells that has 5 or 6 different grits.
Keep those lugs greased afterwards!

BP
 

MagnumManiac

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Joined
Feb 25, 2008
Messages
3,148
I use valve grinding paste. It comes with coarse and fine grit.
Start with the coarse grit and finish with the fine grit. I aim for 90% clean up on the non touching lug and full contact on the touching lug. You can go further, but I have never found an increase in accuracy.
If the action/barrel is bad from factory, I rip the barrel off and true everything anyway and re-barrel.
I only lap the lugs on very accurate rifles from the factory, doing so on a mediocre rifle is pointless IMHO.

Cheers.
 

stangfish

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Dec 31, 2008
Messages
224
Thanks gents.

MM,this is for a Remington long action hunting rig. A long time ago I used some clover leaf, it embeded in the lugs and abutments and made a mess of the faces. Had to recut the lugs and abutments from the scars. Trigger timing was altered and the results were less that adequate. What brand do you use?
 

tobnpr

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Joined
May 30, 2013
Messages
248
I had some 2-4 micron diamond lapping compound from a job I did and used that. It lapped the lugs in fine but it put a mirror finish on the abutments and lugs so now it squeaks when you operate it without lube. What grit or micron do you use? Thanks in advance.

That's crazy xtra fine grit- more of a fine polishing compound. Five to ten thousand grit- you must've not had to remove much material. I can't imagine trying to remove any measurable amount of material with a compound that fine.

Where I start depends on the amount of lug contact. If I'm seeing very little, I'll usually start with 600 grit (if I don't decide to just chuck it up and true them on the lathe). As the Dykem confirms more contact, I'll drop to 400. I don't go any finer than that.

Goes without saying but I'll say it anyway for the benefit of anyone thinking about it- if the current barrel is to be re-installed after lapping be very careful about not going too far with this. There's only about .004 between "go" and "no-go"- and by definition you're increasing headspace, and you're also removing some amount of primary extraction when you do this. If the layout fluid shows minimal contact on only one lug and the barrel is not being replaced I would leave it alone unless you've got a lathe to re-work shoulder and bolt nose clearances after.
 

Alex Wheeler

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Joined
Jul 5, 2017
Messages
1,283
Location
Montana
Lapping is for matting parts that are all ready fitted well. It comes after the grinding process in the steps of fine fitting parts. Lapping lugs should be to remove tenths not thousandths. Theres issues related to lapping so you want to keep it to a minimum. I would stay away from diamond. Its very hard to prevent it from imbedding and continuing to lap long after you dont want it to. You should never run an action without grease on the lugs, thats asking for a gall. 600-800 silicone carbide is a good choice.
 

MagnumManiac

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Joined
Feb 25, 2008
Messages
3,148
Thanks gents.

MM,this is for a Remington long action hunting rig. A long time ago I used some clover leaf, it embeded in the lugs and abutments and made a mess of the faces. Had to recut the lugs and abutments from the scars. Trigger timing was altered and the results were less that adequate. What brand do you use?
I use a brand called Hoyt’s, it’s non embeddable and water based, cleans up very easily.
Sorry, I missed your reply.

Cheers.
 

jrock

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Joined
Mar 12, 2014
Messages
1,239
Location
Idaho
I'll start with 600 grit and see how it cuts. I'll change grits depending on how much I need to remove. I like to end with a product that gives a 'shiny' surface. I've used JB bore paste as well as other 'chrome' polishing compounds.
 

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