lapping lugs

S

shdybrady

Inactive
The off season is approaching for us and this ia when I usually tear down my guns and tinker. This year I am starting to get alittle bit more ambitious with my projects. I have a marlin .17hmr and a model 700 .270 I am wanting to check the lugs for contact.

How do ya'll feel about the shell cut in half with a spring in the middle method? From what I have seen it keeps you from having to remove the barrel which caught my eyes because I dont have the necessary equiptment to do so. I was going to check the lugs with layout fluid, lap the surfaces with 600 grit compound until I get 75% contact and throughly clean out the action to remove the compound. Has anybody used this method?
 
Of course, If the guages indicate the headspace is out of spec. I put the tools down, contact a gunsmith and accept I am out of my league. But, I do want to at least try. I realize it would be easier to let a gunsmith do it from the start. But, to me knowledge is worth more than the price of a dollar
 
What good is 75% contact? It's probably close to that now, most people who have their lugs lapped want full contact....usually a Smith does this before barreling.
Also I've heard some respected members here say it matters not to have lugs lapped....
And your hands and your arm will be wore slick before you lose headspace of any concern using 600 grit.
 
Reason I decided 600 grit is just to control how much I am taking off. I didn't want to be over ambitious with it and take too much off. I cant say definitely that I don't have 75%, because I haven't checked it. But I have heard a fair amount of people saying they had 10-30% percent contact on the model 700. Of course I do plan on checking before hand.

Has anyone tried the shell cut in half method?
 
When I started building Mausers in 2002 I cut a brass case in half, put a coil spring in it, and valve grinding compound on the lugs. I pushed and pulled up and down on the bolt handle until some of the di-chem came off the surfaces being lapped.

I did a couple rifles that way in 2002. I build 3 or 4 rifles per year for myself, and have not been lapping.

What I run into is gun culture accuracy improvement rituals that have improvements so small, I cannot detect or measure the improvement. So I give up. I make enough rifles that are sub 0.5 moa with no wind at the range.... so any more accuracy would be academic when hunting in wind.
 
It sounds like you want to lap the lugs just so you can lap the lugs. How do the rifles shoot now, and what degree of improvement do you expect?

Jim
 
I have to go with Clark and JamesK, I have also found lapping lugs a waste of time. The ultimate folly is guys that lap the lugs on a build and then send the receiver out to be re-heat treated. If lapping the lugs makes a noticable difference, I would have to say you have other problems.
 
Im not just wanting to lap lugs. I am going to first check to see ifbits needed. But before I send off 4 bolt actions, again if needed, I might as well see if its something that I can handle. I have it somewhat made up in my head I can do this. Now if its needed is yet to be seen. Im waiting for my layout fluid to get here.
 
Gunplumber,
I think we are on the same page.

I never fell for the re heat treat in Kuhnhausen's Mauser book, but I did buy the book Dec 12, 2000.
I did not like the few pages of the book and gave it to my brother.
He is the one that made the spring loaded case for lapping. [I think he did another one in 2015]
He trued a bolt face to get rid of primer leakage erosion. [mistake].
He made a mandrel and trued the large ring face. [I fell for that too]

That is THE worst gunsmithing book I ever bought, out of ~50.
And yet Kuhnhausen books on double action Colt revolvers are the best gunsmithing books I ever read.
 
I had an old book that was about barrel making, but the exact title escapes me. I would have to say some of the methods were somewhat crude, but attribute that to the time it was written. It was kind of a cross between a machinist and gunsmith manual. It was really a handy little book and I misplaced it somewhere along the line. Does it ring a bell with anyone here?
 
I can see I wrote a review of this book in 2006

http://www.amazon.com/Introduction-modern-gunsmithing-Harold-MacFarland/dp/0064634264

6 of 7 people found the following review helpful
Can't live without that book
By Clark Magnuson on February 8, 2006
Format: Paperback
Sporterizing Mausers?
This book is a must have.

Other things of interest:
He makes sight dovetails in the barrel with a hack saw!
The guy was a real bare foot doctor.

The table of contents:
1 Proper Methods and the right tools....15
2 How to make your own tools and parts...26
3 Diagnosis and eliminating malfunctions .. 47
4 Selecting and working different steels.. 68
5 How to pick the action for your sporter..86
6 Basic ways of improving military actions ..110
7 How to do your own shotgun work..145
8 Altering and improving the handgun ..163
9 How to achieve the best trigger pull ..181
10 How achieve the most accuracy.. 195
11 How to mount your own scopes and sights.. 218
12 Getting better than new metal finishes.. 234
13 Your military rifle an it's sporting stock.. 249
14 How to handle a hundred disassembly problems ..274
15 Commonly used data and reference tables..297
index ..316

The things I have used from this book:
1) How to do a trigger job on a Mauser with Silver solder
2) Inside radius and distance between holes in Weaver scope mounts
3) Thread length, shoulder diameter, thread major diameter, TPI, and type of thread on barrels for different actions.

This is an old writing.
The newer Weaver mounts are not there.
The newer actions, like Rem700 are not there.
The newer cartridges, like .223 are not there.
 
In a Mauser M98 , the receiver is soft steel like 1018. To be serviceble it has to be case hardened. Many wartime M98s are poorly machined and should have lugs lapped so each lap takes half the forces.This i s important for accuracy also. If the lapping is too severe you have the risk of cutting through the case andthe receiver must be rehardened to replace it. This may improve other things also.
Do everything right and you'll have an accurate durable gun .:p
 
I am not a fan of lapping. If the receiver seat to lug contact is 75%, I would leave it alone. Lapping removes the surface hardness. Many, if not most, bolts have hardened lug surfaces. This surface hardness is only thousands of an inch thick, grind that off and you are down to a softer substrate. I quit having lugs lapped after my first stainless M70 target rifle. Enough material was removed that I had galling on the back of the lugs.

This bolt has never been lapped. It is on its third barrel and contact between receiver and lugs has increased over time. This is the only lapping necessary on a well made modern gun: by shooting it.

 
Alright, alright. I'm still going to check my lugs for contact but I actually plan on sending this action off to be blueprinted. But I am going to buy a stock first. that's proving to be a task being the gun combination that I have.
 
There are things you do for competition rifles that are utterly wasted on a hunting rifle.

Don't lap the lugs on a factory rifle with a factory barrel. It's a waste of effort. When the rifle is rebarreled, that is the time to true up the action shoulder, lap the lugs, and true the bolt face to the receiver threads. Then the new barrel can be installed true to it all.

Lapping the lugs and truing the bolt face and shoulder don't do anything for accuracy of the rifle though. What it does, assuming the barrel is installed true, is that reloads are more accurate as the cartridge head is more true than a rifle that has a bolt face off bore with the barrel axis.

If your virgin brass handloads are .50 MOA or less, and your first reloads off once fired brass are .75 MOA, odds are your rifle could benefit from having the bolt face trued to the bore axis. If the barrel isn't true to the receiver tennon threads then it's wasted effort though, any gains in accuracy on reloads will be destroyed at the next rebarrel as it is unlikely to be off bore in the exact manner as the previous barrel.

In the benchrest game where .25 MOA is a huge group, little things like truing the action and barrel are worthwhile. For a hunting rifle it is a waste of time and effort.

Jimro
 
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