lapping lugs

[tobnpr]

Q:

If the multi-point thread cutting done by CNC is "all that", then why are receiver threads often single-point cut oversize when re-barreling to get them perfectly concentric?

[Gunplummer]

Here is my 2 cents. I have made bolts. Square and round. I used 4140 because I had only a furnace to work with. I never had a problem mixing 4140 and cased items together. If you stay around 38-40 RC, you can still go back and machine the warpage out of the bolt. I rarely did this. IF you are case hardening a bolt, the machining is done before heat treating. Now you you are stuck grinding. With a case of .015-.020 deep, it would defeat the purpose of heat treating in the first place. Same with sending a receiver out to be re-cased. It will warp again. That is what heat does to metal. Why bother to lap the recesses in the first place?
I never catered to the paper punching crowd, but did have some guys that would rather hunt groundhogs than deer. The biggest accuracy difference I noticed was the barrel. Sure, it helps to be careful with the little things, but they are just little things. If the little things add up to a problem, time to think about a new receiver.

[Dixie Gunsmithing]

tobnpr, it's according to the CNC setup, the machines precision, tooling, and operation. There are some new machining centers, that have a rotary indexed work holding collet or chuck, so one can machine the receiver's front and rear in the same machine and setup, without removing the receiver. Those are pretty accurate, but any heat treating can still warp it, even though they use special jigs and methods to control it. A good example of a modern CNC machining center, for this, would be like a lathe, which had an indexed rotary chuck that holds the receiver, which can swing the receiver a precise 180 degrees to the tooling, thus doing both ends in one go.

Several of these older gun factories still use many of the older machining methods, since the factory is set up around that and certain models, where they use pretty much the same fixtures and jigs. They are modernizing, but I have noticed that some still use older tooling. Of course, in blueprinting, we're talking about the difference between creating a fine match rifle, and a hunting rifle, that is made as cheaply as possible.

Another problem is the quality of the barrels manufacture, and if they profile the OD, and turn the shank, concentric to the bore. That is why blueprinting generally uses oversize threads, to correct any misalignment, along with boring and re-threading an offset receiver thread.

If you get a chance, watch the Remington Ilion factory video on YouTube. They still use some of that older specialty equipment and methods, or did the last that I know of. Some of those machines were designed and built just for Remington.

[Gunplummer]

You would have to be nuts to bore out a Mauser receiver ring and re-thread it. If I ordered a pre-contoured barrel, I ran it between centers to skim an area to hold on to thread. At the very least, I put a tight pin in the bore to indicate on. Many an old Gunsmith (Good too) used a 60* threading tool on Mausers because he did not know any better. Wonder what that did to bore alignment? A lot of the improvements in the way guns shoot now is often attributed to the manufacturer, when the biggest effect on accuracy in the last 25 years has been powder and bullets.

[Clark]

Dixie Gunsmithing
Holland DVDs:

I like Dixie Gunsmithing posts. I like Darrell Holland. Ok, Ordered the DVD. I have been sporterized Mausers for 50 years, I will get it right some day.

[Dixie Gunsmithing]

Clark, I thought it was Holland in those two videos, but it is Ken Brooks, as I just checked. Brooks covers pretty much everything concerning accurizing in those two videos. If I recall, as I've not watched it in a while, I think he shows how to make that centering mandrel. I know he shows using it in the lathe.

Holland is who recorded the AGI machine shop training videos. Unless they have some new ones, he did the lathe and the mill for them. He is rather particular in being accurate, and a class A1 machinist. The lathe video has 4 parts to it. He has one named: Super Tuning the Factory Rifle, which is AGI 325.

[Clark]

I got instant email response from Holland and I appreciate that.

10/4/2012
I am trying to drill a hole in the receiver for the [recoil lug] pin.
What is the distance from the center of the barrel hole to the center of
the pin hole?
I am having a hard time measuring it, but it is somewhere around .605"
to .608".
I have your standard lug.

[email protected]
10/4/12
Clark, the dimension is .605... Good measuring...
Go forth and do GREAT things, check out our stocks muzzle brakes etc.
Thanks
Hollands

I use his Witches brew bore cleaner, but I am still experimenting with how not to spill it.
I use Holland bags from Dog Gone Good bags.

[Clark]

That DVD is so slow it is hard to watch I know all this stuff.
And it is 20% wrong.
He is going on second hand information about strength. I have done it.
I am giving up after 30 minutes. Maybe I will come back.
He is not a bad guy. I would let him mow my lawn.

[Dixie Gunsmithing]

Clark, yes, Ken Brooks is still wet behind the ears a bit, though he is a former instructor of Gunsmithing at Lassen College. Evidently, he's taking over Bob Dunlap's shop. Holland would be the better one. That video, AGI 325, "Super Tuning the Factory Rifle", of Holland's is floating around to view , otherwise, it is for sale.

[tobnpr]

Hollands' are good peeps.

I've been recommending/buying a lot of their brakes for customers' rifles. Quality products, effective. Talk to a live person on the phone to order, like the "old days", lol...

[Dixie Gunsmithing]

tobnpr, Yes, I have a good bit of respect for Darrel Holland. He's very well educated on firearms. AGI couldn't have picked anyone better to teach their machining courses. I like Gene Shuey, too, especially his stock work with oil finish. He does them as I do, or pretty close to it.

[Carriertxv]

Are all of the AGI videos done with such poor quality? I have watched a few online and they are just terrible. Great content but very bad picture quality.

[Clark]

This is good:
Gunlab re barrels a Mauser
https://www.youtube.com/watch?v=1Ufes_zrZmg

[Dixie Gunsmithing]

Carriertxv, Most of those videos are actually quite old, and were on video tape; VHS to be exact. When DVDs became popular, the started to convert them to that format, thus you have a grainy image, which is to be expected. Their Gunsmithing course used to come in a big box, packed full of VHS tapes. The only problem with AGI was, that they weren't accredited, and may not be now, I'm not for sure.

The last recent video that I saw, with Bob Dunlap in it, showed that he was getting a good bit up in age. That was a video where they were exploring if excessive headspace would cause an explosion. My guess is that he's in his 70s now. The ones that show him with the cut-away guns, was just after his retirement as a gunsmith instructor at Lassen College in 1995. He started at Lassen around 1971-72, and ran a gunsmithing shop on the side.

[tobnpr]

This is good:
Gunlab re barrels a Mauser

Funny you mention that one...
It is an excellent video IMO- when I started on my self-taught machining journey, this was one that I held in high regard. Covers basics very well.

In the end, I suppose all of us that learn this way spend hours and hours online, gathering all the info we can, then sorting through and deciding what makes sense for our particular machines, and applications.

I guess I shouldn't have been surprised to learn that there is absolutely no consensus on the "best" way to ream a chamber!

[Clark]

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

[Dixie Gunsmithing]

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.

[Clark]

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.

[Shimpy]

"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.

[tobnpr]

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.

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

I'm just gonna keep moving the goalposts.

[Unclenick]

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.

[zplinker]

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.

[Gunplummer]

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.

[Unclenick]

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.

[Gunplummer]

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.