This Springfield action shows the wear from the bolt and a little set back. There is .005 difference between the bottom and top lug. This is mostly wear, there is no telling how many rounds have been fired through it, but I would say a bunch.



Jack Belk posted a picture of a Mauser that had been opened up to accept the 375 H&H. The receier was opened up in the front, by cutting the front ramp wich weakened the bottom lug causing a severe bulge in the ramp that you could see and feel with your finger.



The best way to find out how much wear or set back is to pull the barrel and measure with a depth mic.



The receiver lugs can be trued up, but the bolt lugs will have to be trued as well and then lapped together.



Depending how much metal is removed may require heat treating to harden the metal and reduce wear.

Allen,

I appreciated our converstaions on this subject at the Sportsman Show a few weeks ago.

I saw in another tread (maybe this one a few posts back) that when lapping the lugs for contact, you might affect hardening by wearing through the surface, into 'soft' metal.

In your experience is this likely? If so, how is it prevented? I wouldn't think that you could lap then harden. But then again, what the hell do I know?

Take Care,

-Steve

To answer the original question on how to measure with the barrel still on, only one way I know of. The best way of course, is to remove the barrel but short of that, here goes. With the bolt stripped, including the firing pin assembly and extractor and collar out, insert a "go" gauge in the chamber and the bolt in the receiver and position a dial indicator at the rearmost portion of the bolt body and "Zero" the indicator when closing the bolt (not closed yet. You only want to identify the high spot). Next, closing the bolt on a "go" gauge, observe the indicator while pushing the bolt back and forth in the receiver with the handle in the down position. What this gives you is the amount of setback between the "closing" position and the "closed" position. Simply using a "go" or "no-go" guage won't give you an honest reading; it will only tell you what headspace you have when closing the bolt over the high spot and not the low spot in the closed position. Any questions?

Jim

I have a limited idea what setback is, but lotsa questions. What are the causes? How can you tell if an action is 'set back?' Will an action show excessive headspace when go/no go gauges are used? Is the action ruined when set back is present? Thanks in advance to the Mauser experts. Bob

I am sure some expert smiths will join in with this discussion, but I will speak from experience in having a close friend that had a rifle that developed setback. It was an FN action with a 25.06 barrel, and I was able to look at it.

Setback is generally caused by a dimensional change in the steel of either the locking lugs on the bolt, or the locking recesses in the receiver. When you first barrel the receiver, you have a certain amount of headspace (it is measured differently for different types of cases)so that cartridges will reliably feed. If the lugs or the recesses wear, the headspace increases. Generally speaking, (I may be incorrect on this) I believe that one can get away with headspace of about 6 thousands, and maybe even a bit more. But say you had another 6 thousands wear on the bolt lugs so now your headspace was 12 thousanths. Now, when you fire that gun you have the cartridge blowing back without support just a tiny bit more, but enought to cause a spike in pressure inside of the gun.

With my frieds 25.06, he noticed it because extraction started to get harder, which caused him to check his fired cases. They were developing little tiny bulges right next to the rim. He then used guages, and Sure enough, his headspace had increased enough so that he could just barely close the bolt on a no go guage.

What he ended up doing was to take the barrel off. Looking at it, one could see the wear pattern on the locking lug recesses, but to tell you the truth I couldn't feel anything much different when I ran my fingers over it. He had to trim some barrel off, relap the lugs, and reinstall the barrel and reream it. It now shoots very well once again.

Some cartridges have their headspace measured from what is called a Datum line, others from the belt, and others from the rim. Suffice it to say, the bottom line is that you don't want a sloppy chamber where the cartridge has a lot of room to move around!!!

So, what are the characteristic signs? Garden variety pressure signs like case expansion? What about case stretch? Primers backed out? Bob

a lot depends on what cartridge you are using, and what type of round you are using. My friend was using a 25.06 with some pretty hot reloads and the first thing he noticed was that extraction was getting a bit harder, whereas I doubt that you would notice anything if you were using 8mm mauser factory loads. Suffice it to say, the best way to check is to own a go guage and a no go guage for each rifle that you shoot.

Blue

There are surprising number of new-condition, original military and commercial Mausers that exhibit lug setback, and many of these rifles were only test fired at the factory. Even certain factory/semi-production rifles based on FN Mauser actions (like pre-Mark V Weatherbys) show measurable seback.

For my money, Mausers (if you plan to shoot 'em instead of look at 'em) need to be sent out and rehardened by a specialist, and if a riflemaker refuses to have this proceedure carried out, I'll take my business elsewhere, pure and simple.

I asked riflemaker David Miller about reheat-treating/ rehardening actions, and his answer was "ALWAYS!"

AD

The type of set back I'm concerned with has not been discussed here in great detail. That is set back into the action by the bolt. I believe I have experienced this at least twice.
1.When my son came back from Desert Storm in "91" I gave him a .308 sporter I had fashioned for him out of a 1916 Mauser. I figured if some government is retrofiting small ring Mausers to accept the .308 cartridge they must know what they are doing. Before we took it to Colorado deer hunting we did the range thing with a bunch of mediocure reloads. No problem. After we came back from the hunt we ran a bunch of Velencuelian military ammo through it. After only a short while I noticed the bolt handle was getting harder to lift with every shot. After that loads that had given us no trouble before exhibited the bolt handle lift problem.

2.I have experieced the exact same problem with a 22-250 I have that went through a rather severe over pressure. I have replaced the bolt on it but if I fire a slightly greater than a modest load again the hard bolt lift.

The rubbing of the bolt face against the rear of the case is obvious.There is no extrusion of brass into either ejector slot. No flattened primers. no stressed heads or expansion. On the 22-250 there is a possibility of the bolt face not being perpendicular to the bore line but on the .308 I doubt it. All of my range reloads are loaded to just close so head space can be ruled out. One of my questions is; with the barrel on how can action set back be detected? And next what can be done to correct it? roger

Blue,
I read that book, over and over again.
It is organizationally scatter brained.
So am I.
I do better with orderly books.

I did get the inspiration from that book to make receiver truing mandrels and inner stop ring lapping fixtures.

I am not sorry I bought it, just sorry his editor didn't give him some discipline.

It all looks to me like class lecture notes taken out of a note book, and sent to a publisher with no additional effort.

Gunsmither

I have also seen actions where the only bearing point was a very tiny bump one of the lugs. So I am sure that you would agree with me that lug contact has to be checked, and if necessary the lugs to have to be lapped to make sure there is good contact.

Blue

Lapping the lugs on a Mauser action was most likely what caused the setback in the first place, as these actions were carburized, or case hardened. When you lap the lugs, you cut thru the case hardening somewhat, and possibly too much, allowing the metal to be swaged in by the pressure of firing repeated rounds, eventually causing grossly excessive headspace. There is no way that I know of to tell how deep the case is, short of sectioning.

I have seen a number of Mauser style actions with severe lug setback due to lapping. Jerry Kuhnhausen, in his fantastic book on the Mauser actions, insists that Mauser style actions be re- heat treated after lapping. I agree.

For safeties sake, I'd recommend not using an action that has been lapped without re- hardening the lug areas. Safe Shooting Friends! -"gunsmither"