Gunsmithing Lapped lugs look good?

[3-0-hate]

First time lapping lugs myself. Just wanted to check to make sure it looks like I have full engagement on both lugs and also ask if I should switch up to a jewelers rouge to polish the engagement surfaces a bit or just leave it be and let it self "polish"?

Thanks for looking.

 

[eklarsen]

Put some sharpie on the lug bearing surface and run it through a couple of cycles and see if it wears off evenly.

 

[3-0-hate]

Put some sharpie on the lug bearing surface and run it through a couple of cycles and see if it wears off evenly.

Thanks for the advice.. I only have sharpie missing on one lug.. the other one looks untouched...

Do I just need to keep lapping until I get even engagement on both lugs with the sharpie test then?

 

[Supersubes]

Thanks for the advice.. I only have sharpie missing on one lug.. the other one looks untouched...

Do I just need to keep lapping until I get even engagement on both lugs with the sharpie test then?

What do you mean, clearly both lugs are contacting from your pics? No, don’t lap the shit out of it.

 

[3-0-hate]

What do you mean, clearly both lugs are contacting from your pics? No, don’t lap the shit out of it.

The sharpie only wore off on one side.

 

[deadly0311]

Are you rebarreling the rifle? Your last picture shows you only have contact via one lug.
How did you go about lapping it? Just pull the barrel and went to town or what?

 

[Praeger]

Did you use marking fluid/sharpe before lapping your lugs? What made you decide to lap them?

 

[3-0-hate]

Are you rebarreling the rifle? Your last picture shows you only have contact via one lug.
How did you go about lapping it? Just pull the barrel and went to town or what?

I pulled the barrel off to replace a modified recoil lug (tube chassis mod). I screwed the barrel in, inserted a fired case into the chamber and lapped it that way.

Did you use marking fluid/sharpe before lapping your lugs? What made you decide to lap them?

It has always had one lug with no finish and one lug with finish.. Decided to lap to make lug engagement more uniform.

 

[Praeger]

It has always had one lug with no finish and one lug with finish.. Decided to lap to make lug engagement more uniform.

OK, from the photos it looks like material was abraded from both lugs. It's odd that when you went back with a Sharpe, only one lug made contact.

 

[...]

locking lugs wont always make contact on both lugs if they are not "under load".

 

[3-0-hate]

locking lugs wont always make contact on both lugs if they are not "under load".

Roger. Ill go back and re-check with the barrel and fired case installed.

Thank you.

 

[3-0-hate]

So if I’m still not getting engagement (with barrel, lug and fired case installed) on both lugs, do you recommend I continue lapping? It looks like the left lug is just beginning to kiss the abutment surface.

 

[...]

So if I’m still not getting engagement (with barrel, lug and fired case installed) on both lugs, do you recommend I continue lapping? It looks like the left lug is just beginning to kiss the abutment surface.

no no no no.....go shoot it.

even with a fired case, there is no force being placed on the bolt face.....youll only get that when a round is fired.

 

[Supersubes]

So if I’m still not getting engagement (with barrel, lug and fired case installed) on both lugs, do you recommend I continue lapping? It looks like the left lug is just beginning to kiss the abutment surface.

View attachment 7516561

If you’re lapping with the trigger installed, and you have any clearance at the rear receiver ring(almost all actions do), you’ll only have contact with the lug at 6 o’clock. The trigger is pushing the rear of the bolt up. The 12 o’clock lug will be hovering. This is not the way to lap lugs, as you’ll only lap things into misalignment.

 

[Wannashootit]

You need a lug-lapping fixture to do this correctly.
Screws into the receiver, spring-loaded plunger against the boltface to provide the needed pressure against the lug abutments.

If I understood you correctly, you replaced the recoil lug... that'll change headspace.
Lapping the lugs- that'll change headspace. Unless this a "Remage" barrel, you've changed headspace from both of these actions.

Lug replacement can go either way- did you mike the new lug and compare against the original?
Lapping the lugs will only increase headspace- which is why it's always done before the needed measurements are taken for chambering.
You never want to lap lugs on an action with a shouldered barrel that has already been fitted.

 

[smoothy8500]

I screwed the barrel in, inserted a fired case into the chamber and lapped it that way.

Wouldn't the ejector provide the tension unevenly to one side only?

 

[3-0-hate]

The new lug is 10 thousandths oversized and will be machined to correct for any headspace issues.

 

[Hateca]

Do not use the barrel as a guide to lap. Do not use a fired case to lap. Do not lap with the firing pin assembly and trigger installed. Do not lap with ejector installed. Get and use a lapping fixture or some way to apply even pressure to the bolt while lapping. When done correctly it should only take a few min. Any longer something is wrong or your set up is not correct.

BTW I’ve seen rifles with only contact on one lug shoot light out so it’s not the end all be all of accuracy. I’ve purposely did some crazy machining ops to a receiver to see just how bad a receiver can be with a custom barrel and still shoot tight groups. You would be shocked how bad a receiver can be. In fact you are wasting your time if this is a factory barrel and an un-trued receiver. Your accuracy is going to come from a good barrel with a chamber that’s been cut correctly.