lapping lugs

The gun labs guy, with his bent barrel theory, his feeler gauges, it was just like me.... until the end when he tightened the receiver while the barrel was still in the lathe and the barrel slipped. I have enough trouble with barrels slipping in the lathe without that. I take the barrel out and put it in a real barrel vise for the last 0, 1, or 2 thou.
There are a lot of terrible gunsmithing videos with a lot of views, but that gun labs guy deserves his 400k views. And his Forgotten weapons videos have gun information that is news to me.

Another guy making some great gunsmithing videos on youtube is Larry Potterfield..... suprise. He switching to paid shipping ~ 2001, and went to Africa with antique Winchesters until the pain was over. I thought he was just a biz man.

Now that Windows 8 and Comcast are not getting along on Windows Media schedule, I am not watching TV on the analog tuner in one of my computers.
I have switched from TV to internet videos.
My father, chief engineer with a list of 100 things to do per day, drank coffee in the morning and booze at night, like jumping on the accelerator and then the brakes.
I get ~ one thing done per day... and watch boxing vids to get going and physics vids to get sleepy.

Gunsmithing videos are better for mid day viewing
https://www.youtube.com/watch?v=35c6BqxpYSs
 
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Clark, from the pressure that I could see the military putting on your father, I could see a few stiff drinks being required every evening, myself. If things do not happen as compared to the higher-ups schedule, which it hardly ever does in engineering, I could see him being either a nervous wreck, or about to blow a gasket, each evening.

When I worked in the engineering dept. of our local mining machine manufacturer, several of us stopped by a local bar for one or two stiff drinks before heading home. Not enough to get drunk, but enough to calm the nerves over a couple of days each week. We used to joke, and say it was over not having to sit in the quit time traffic. Sometimes, you just want to choke schedulers.
 
We raised our two kids without either ever seeing ME intoxicated, but our daughter did make fun of my amateur gunsmithing, insinuating that none of my guns work.

My wife is 60 and still does over 60 hours a week of engineering. I have not bothered working since Nov 2008. I keep telling her that a 60 year old race car should not be pushed to the limit every day at the track, but carefully maintained and putt along in a parade.
 
"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?"


Lapping works by the abrasives imbedding into the softer material and cutting the harder material. You could never get rid of the compound by cleaning once they are imbedded. Laps are used and then discarded.
 
I keep telling her that a 60 year old race car should not be pushed to the limit every day at the track, but carefully maintained and putt along in a parade.
Click to expand...

Damn, Clark...
Don't you know that 60 is the "new 40"?? :D

I'm just gonna keep moving the goalposts.
 
Shimpy,

It can work that way, but doesn't have to. Ever lap valves for an engine? There's no embedding involved, as the mating materials are too hard. If it did happen, the valves would wear out fast. Same with carburized receiver and bolt surfaces.
 
One of the worst examples I've fooled with was a 700 Rem. in .257 Wby. which had only one bolt lug making contact. The other was .015" off. The rifle was returned to Rem., where it was proclaimed to be just fine, yet it shot 2" groups at 100 yards. After cleaning things up, and with a new barrel, it shot in the .1's, at 120 yards. Was it all the new barrel? I think not! Tried to add the target pictures, but am not set up for that.
 
Probably was the barrel. I picked up a sporterized Krag years ago that needed a little work on the stock yet. That rifle was awesome at 100 yards with the factory shortened barrel. Think it would have been better with two lugs? I have seen rifles that shot better than 2" at a hundred yards that had REAL problems. Barrels and bolt faces so out of alignment that the fired brass stands at an angle when sitting on the base. I will never be convinced that lapping lugs on a used rifle is anything but waste of time.
 
What matters to precision (group size) is repeatability. A one-lug rifle can shoot just fine if it is consistent. I've also seen a rifle whose chamber was angled 0.007" off the bore axis at the breech end, and it shot like a house on fire, but only with new brass. For reloads you had to orient the case in the chamber the same way it was fire-formed (out of square) by the previous firing.

Where a one-lug contact gets into its worst accuracy problem is when typical firing pressure is turning it into a a one-and-a-half lug gun. That is, the uneven contact is in the process of flattening out at around normal firing pressure. In that case, typical shot-to-shot pressure variance is actively varying the degree of lug contact, which can introduce stinging on the target.

Squaring up (blueprinting) a receiver and lug contact increases the odds that a rifle built on that receiver will group will, but it isn't the only possible good arrangement. The deal with lug lapping is to try to eliminate that partial contact situation arising. 75% is just a sort of general guess at enough contact that shot-to-shot variation will not significantly vary the location of any recoil moment associated with uneven lug contact. Unfortunately, you can have other problems that introduce an issue anyway.

There are different theories about how best to set the bolt position up for lapping. Some say you should center the bolt in its receiver way so contact under pressure doesn't make the bolt favor one side of the way. Others point out the pressure from the cocked striker will tend to lift the bolt over the trigger anyway, so you should lap it in that position and true the bolt face for that position, while the straight truing guys say that will induce rebound of the bolt off the way and introduce a new barrel deflection factor. I expect each method has guns in which it is better.
 
So much for the neck sizing horse crap. I have said the same thing about orientation for neck sized brass for years. The key word here is "Used" rifle. You would probably be better off squaring the bolt face up on most military reworks.
 
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