Gunplummer
New member
There you have it. If you get a noticeable difference just from lapping the lugs, something else is wrong.
lapping lugs
- Thread starter shdybrady
- Start date
Jimro is spot on.
Waste of effort on a factory rifle.
You can lap the lugs 'till the cows come home- if the bolt when in battery isn't true to the central axis of the bore, if the chamber isn't cut concentric to the bore, all the things that make up a precision, trued barreled action- it's not going to matter a bit, and might make accuracy suffer.
It's part of the big picture, never a "standalone"...
Waste of effort on a factory rifle.
You can lap the lugs 'till the cows come home- if the bolt when in battery isn't true to the central axis of the bore, if the chamber isn't cut concentric to the bore, all the things that make up a precision, trued barreled action- it's not going to matter a bit, and might make accuracy suffer.
It's part of the big picture, never a "standalone"...
If I may suggest,consider the machining operations of making a bolt,and of cutting the locking shoulders inside the receiver.
Wouldn't both of the rear faces of the bolt be cut in the same pass?
Same with the milling inside the receiver.
I would expect,as cut,to see little if any variation side to side.
Other variables enter in later,but as machined I would expect variation to indicate well less than .001.
I say that because its important to understand the scale of "lapping"
It should be a few tenths worth of tool finish.
Under those conditions,neither headspace or surface hardness are an issue.
Lapping is not the method to take out .002 or .003.
It CAN happen that the receiver bore and locking lug recesses are not perpendicular.or a similar condition with the bolt.If the bolt is "tilted" one lug can be lifted.
Funny thing,if you pull back on the bolt handle to lap the lugs,you create this condition with the off center load.
Another source of trouble post machining is the polishing wheel.One lug can be overpolished,compromizing the machined part accuracy.
Check it if you must with some sharpie or cold blue on the bolt lugs.The load must be in the center of the bolt face.
If you see that a lug does not bear...well.I might not like that either.
But lapping a finished rifle is somewhat like putting on your sox after you tie your shoes.
There is an order to these things.
Spooning valve grinding compound into the receiver is not the answer.
I have my own way of hard fitting parts to bear.I only want to take the peaks of the high spots.I want to take nothing off the low spots.
Cold blue,shiny spots,and small strokes with a very fine hard stone,only cutting the shiny spots,will make the shiny spots get bigger.
Wouldn't both of the rear faces of the bolt be cut in the same pass?
Same with the milling inside the receiver.
I would expect,as cut,to see little if any variation side to side.
Other variables enter in later,but as machined I would expect variation to indicate well less than .001.
I say that because its important to understand the scale of "lapping"
It should be a few tenths worth of tool finish.
Under those conditions,neither headspace or surface hardness are an issue.
Lapping is not the method to take out .002 or .003.
It CAN happen that the receiver bore and locking lug recesses are not perpendicular.or a similar condition with the bolt.If the bolt is "tilted" one lug can be lifted.
Funny thing,if you pull back on the bolt handle to lap the lugs,you create this condition with the off center load.
Another source of trouble post machining is the polishing wheel.One lug can be overpolished,compromizing the machined part accuracy.
Check it if you must with some sharpie or cold blue on the bolt lugs.The load must be in the center of the bolt face.
If you see that a lug does not bear...well.I might not like that either.
But lapping a finished rifle is somewhat like putting on your sox after you tie your shoes.
There is an order to these things.
Spooning valve grinding compound into the receiver is not the answer.
I have my own way of hard fitting parts to bear.I only want to take the peaks of the high spots.I want to take nothing off the low spots.
Cold blue,shiny spots,and small strokes with a very fine hard stone,only cutting the shiny spots,will make the shiny spots get bigger.
Dixie Gunsmithing
Moderator Emeritus
The receiver is milled and broached in several steps or operations. However, the front, where the barrel thread and lugs are machined, are done in one or two operations, and the rear of the receiver is machined in another. That is why there can be a variance in concentricity and longitudinal alignment. This is why that blueprinting is done, using the bores center line, so the front and rear will be closer to matching it. Here, you use a centering mandrel, in the rear of the receiver, to machine the front. AGI has a good video about doing this, by Darrel Holland (see below).
The factory operations are all done in jigs and fixtures, mounted on the machines, and though they try to get them as close as possible, there are some variance over the several operations. The use of CNC machining has gotten some of them closer, but it depends on what the designer chose as far as tolerances, even on these.
Not-Holland [Ken Brooks] DVDs:
http://www.midwayusa.com/product/676718/american-gunsmithing-institute-agi-video-how-to-rebarrel-tune-and-blueprint-military-bolt-action-rifles-2-volume-set-dvd
Edit: That is Ken Brooks in those two videos, and not Darrel Holland. Brooks is an instructor at Lassen College Gunsmithing School.
The factory operations are all done in jigs and fixtures, mounted on the machines, and though they try to get them as close as possible, there are some variance over the several operations. The use of CNC machining has gotten some of them closer, but it depends on what the designer chose as far as tolerances, even on these.
Not-Holland [Ken Brooks] DVDs:
http://www.midwayusa.com/product/676718/american-gunsmithing-institute-agi-video-how-to-rebarrel-tune-and-blueprint-military-bolt-action-rifles-2-volume-set-dvd
Edit: That is Ken Brooks in those two videos, and not Darrel Holland. Brooks is an instructor at Lassen College Gunsmithing School.
Gunplummer
New member
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.
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
Moderator Emeritus
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.
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
New member
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.
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Dixie Gunsmithing
Moderator Emeritus
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.
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.
Dixie Gunsmithing
Moderator Emeritus
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.
, otherwise, it is for sale.Dixie Gunsmithing
Moderator Emeritus
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
New member
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.
Dixie Gunsmithing
Moderator Emeritus
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.
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.
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!