excessive headspace, rechamber without barrel setback?

[bruss01]

I have a swiss Schmidt-Rubin (89-11, I believe) that was sporterized by the import company back in the sixties. Now, the purists will consider this rifle a piece of trash because it isn't "all original condition" but you have to see this beauty to appreciate it. It's PERFECT in every way. And it's nearly 100 years old. It's the only rifle in my collection that my wife thinks is truly beautiful.

But we have a problem in paradise. The importer re-chambered the barrel in .308 winchester. Keep in mind, this is the ORIGINAL barrel we are talking about, since 7.5 Swiss and .308 winchester share a common diameter. The barrel still has the original serial number stamped on it near the receiver. Now, pay attention to that because it's important. This rifle, at the range, was exhibiting a problem where the brass was extremely hard to extract, requiring a mallet. Two shots of that is enough, so off to the gunsmith we go. The gunsmith diagnoses excessive headspace, and refused to cut a new .308 chamber because he says the old metal isn't up to the pressure. Ok, so I ask what about re-chambering it back to the original 7.5 Swiss? He humms and hawws and I let him think about it/ make some calls/ think about it some more. He comes back 2 weeks later and says he can't do it. I believe he doesn't have the skills, or the tools, or the profit margin to get it done (maybe a combo of all 3). The kicker here is that I don't want to lose the original serial number stamping on the barrel, meaning I don't want to swap out the barrel and I can't trim much (it's pretty darn close) off the receiver end of the barrel.

Suggestions? Comments? Any leads to someone with more knowledge? I know a 7.5 swiss chamber reamer is probably not the most common tool on a gunsmith's bench. I don't mind sending it off if it will get top-notch attention.

 

[jpcampbell]

It could be any one of those three reasons you gave or, maybe it can't be done because it isn't safe, or possible. If you have no faith in your gunsmith take it to another professional smith and ask him, but be sure he has lots of experience with re chambering. Why cant you put on a new barrel and have the serial numbers put on it?

 

[bruss01]

jpcampbell : It could be any one of those three reasons you gave or, maybe it can't be done because it isn't safe, or possible. If you have no faith in your gunsmith take it to another professional smith and ask him, but be sure he has lots of experience with re chambering. Why cant you put on a new barrel and have the serial numbers put on it?

Jpc - I don't know what the reason is. My experience with gunsmiths in my area is that while most of them are competent with common hunting rifles, most of them do not want to deal with more esoteric firearms - i.e. something not a Winchester or a Remmington. They probably do not have the clientele to support justification for purchasing the tools and acquiring the skills to work on SKS's or Straight Pull Swiss rifles or anything out of the ordinary like that. I can acknowledge that as a simple business decision, not as a slight against anyone's abilities. However, I'm just as certain that somone, somewhere, has the tools and the talent needed to get the job done.

As far as it being safe, that was the justification not to rechamber it in .308, because it couldn't handle the pressure. But the rifle was originally built in 7.5 Swiss, so it does have the ability to handle that pressure level. This should be safe and I was given no information to the contrary by the smith.

Why not just change the barrel? Yes, I do have a reason. That was the smith's suggestion. I do not want to do that because the rifle is all original parts. Yes, they have been modified by the importer, but all the original parts are still there. It is a work of beauty. You will never get a finish on a new barrel to exactly match the old receiver. If the only option is to change the barrel, then I will have a working rifle that is no longer all original parts and doesn't look good. As is, I have an all-original parts rifle that is beautiful but can't be fired. If the goal was just to get the rifle working, heck, that would be easy. But the goal is to get the rifle working with the original parts without defacing it. That's why I'm soliciting input here, because all the EASY answers just don't work for me, and I need a higher level of knowledge to achieve my goals for this beautiful old antique.

 

[mrkubota]

Why not just make your own custom brass?
Do a chamber cast and use some .30-06 cut down to the necessary length.
Then FL size them with your .308 die to the set the shoulder properly.

Alternatively, you could try fire-forming some new .308 brass without the projo. That should let the brass 'grow' to fill the chamber properly too.

 

[Jim K]

The .308 cartridge is smaller/shorter than the 7.5 Swiss in just about every dimension except the bore diameter. So it is obvious that your barrel was not just "rechambered" to .308. Either the barrel was set back, some kind of chamber insert was used, or a whole new chamber was installed. Let's look at those possibilities.

1. Set back barrel: If the barrel was not set back, there should be a shoulder ring about 1/8" wide right ahead of the receiver with the last three digits of the serial number on it. If that is not there, or if the barrel taper is already beginning at the receiver, the barrel has been set back. The rear of the sight should be back almost to the receiver also. If the barrel has been set back, rechambering to 7.5 would bring the high pressure area out to or past the thick part of the barrel, an unsafe condition. As you see, that barrel diameter drops off quickly, not like some barrels which have a long chamber area.

2. Chamber insert: If a chamber insert was used, like that used to convert .30-'06 rifles to .308, the fired cases should show a severe bulge behind the shoulder. Maybe the insert can be removed, but it is often the practice to glue those inserts in after roughing that part of the chamber. If that was done, the original chamber is ruined and a 7.5 chambering reamer won't clean it up. If the insert is removed and the chamber is OK, you lucked out, but you won't know until you remove it. If removing it ruins it (quite likely) it can't be put back in, so you could have a rifle that neither caliber will work in.

3. New chamber: This was done on some 7x57 rifles converted to .308. The barrel was rebored and re-rifled, then the breech end of the bore was drilled and reamed to take a 3/4" (about) plug which was driven in, soldered or glued in place, and then reamed with a .308 reamer. This was sometimes done in South America to convert old rifles to 7.62 NATO for reserve use, with the understanding that they would probably never be fired again and certainly not more than a few shots. There is often a distinct gap between the original barrel and the new chamber, providing an area into which hot gas could leak and erode.

A set back barrel can be seen from the outside, the others with a bore scope. I would not try to re-chamber any of them back to the original caliber for safety reasons.

I don't know why your gunsmith balked, or what he saw. But I am inclined to believe that he declined the work for good reason, not just some kind of prejudice against surplus rifles, and for some reason was unable to convey his concerns to you.

Jim

 

[Big Az Al]

Rebarrel

bruss01

Why not just change the barrel? Yes, I do have a reason. That was the smith's suggestion. I do not want to do that because the rifle is all original parts. Yes, they have been modified by the importer, but all the original parts are still there. It is a work of beauty. You will never get a finish on a new barrel to exactly match the old receiver.

Learning what it takes to Match diferrent finishes is always a work in progress.

But do not insult those of us that have decades in doing polishing and learning, trying and matching! Can everybody that does refinishing do it? probably not, but it should be surprising how many are able!

 

[bruss01]

1. Set back barrel: If the barrel was not set back, there should be a shoulder ring about 1/8" wide right ahead of the receiver with the last three digits of the serial number on it. If that is not there, or if the barrel taper is already beginning at the receiver, the barrel has been set back. The rear of the sight should be back almost to the receiver also. If the barrel has been set back, rechambering to 7.5 would bring the high pressure area out to or past the thick part of the barrel, an unsafe condition. As you see, that barrel diameter drops off quickly, not like some barrels which have a long chamber area.

Jim, thank you for that excellent information. I believe the barrel has been set back to some degree (not sure how much) and a new chamber reamed by the importer. The barrel does not appear to have been bored. I don't know if there is an insert, I will check. Maybe there is a photo I can post here for opinions. Again, thanks for the input!

Ok, found the pic - here's the barrel/receiver joint. It looks like that band you mentioned is still there, so maybe we have some room to work?

 

[frogomatic]

I know of a lot of gunsmiths that won't touch a job like that, not becuase they can't or it isn't safe, but becuase of cost and difficulty in replacing said rifle should somthing go wrong. Most of em won't do it, because they won't risk Fing it up and having to buy you a new one.

 

[coelacanth]

I think the idea of the chamber cast is a good one. . .

most any gunsmith should be able to handle that one if you don't feel up to doing it. While they are at it have them slug the bore so you know just exactly what dimensions you are dealing with in both the chamber and the barrel. A good borescope will likely show whether a chamber insert was used and also what condition the bore is in to great detail. You may have to custom load your own ammo to get the rifle to perform up to its potential but considering the potential of the Swiss rifles it is likely worth the effort.

 

[bruss01]

Thanks for the tips and input, folks.

From what I am hearing, it is starting to sound to me like:

a. - the barrel apparently was NOT set back
b. - probably a chamber insert was used to convert
c. - the insert may have FALLEN OUT? leaving a chamber that is rough and oversized for the .308 round? Leading a to a cursory diagnosis as "excessive headspace?

But I would have thought that would be OBVIOUS to any gunsmith worth his salt? And why he would not mention this to me in assessing the rifle? Curiouser, curiouser....

But even that scenario wouldn't explain why the rounds fed and fired without issue. Maybe the extractor held it tight enough to the bolt for the firing pin to do it's job? I have only ever fired the two rounds from it, so I can't speak to reliability, but is this possible?

I get the gun back today, I will have to find somewhere to send it to have the examination done by someone who knows what they're looking at. For a metro area, I'm surprised that we have such a dearth of people who are GOOD at working on guns, at least guns that are not common hunting firearms. I had a local "gunsmith" (not the current guy) tell me my SKS rifle was an illegal "assault weapon" because it had a "flash hider" and a "detachable magazine". I told him No, that's a LEGAL decommissioned grenade launcher (tube welded over, unmistakable) and a non-detachable magazine (the origninal, quite obvious), which happens to be uninstalled at the moment (was having some trouble getting it back in, that's why I was there). Decided at that moment that I did not want someone that unknowledgeable of the SKS rifle working on my guns, promptly turned around and left.

 

[bruss01]

2. Chamber insert: If a chamber insert was used, like that used to convert .30-'06 rifles to .308, the fired cases should show a severe bulge behind the shoulder. Maybe the insert can be removed, but it is often the practice to glue those inserts in after roughing that part of the chamber. If that was done, the original chamber is ruined and a 7.5 chambering reamer won't clean it up. If the insert is removed and the chamber is OK, you lucked out, but you won't know until you remove it. If removing it ruins it (quite likely) it can't be put back in, so you could have a rifle that neither caliber will work in.

Jim,

Unfortunately, I didn't think to save the brass. That was over a year ago. Just curious, in the chamber insert scenario you mention, if the barrel has not been set back, and the chamber has been "roughed up", is there anything that would prevent setting the barrel back a little bit and reaming a new 7.5 chamber? It looks like we might have some room (see photo). I honestly don't know how much a barrel has to be set back, obviously it would need to be at least one full turn for the sights and the serial numbers to match up again, but how much is that? Of course it would all depend on how serious the "roughing up" is, right? I'm assuming just some "texture" and not any serious gouging (sp?).

 

[rcmodel]

Even finding a 7.5 Swiss chamber reamer would be a major stumbling block, and one primary reason most gunsmiths wouldn't touch the job with a 10 foot pole.

Clymer, Manson, and others I checked did not stock them as a standard caliber.
That means you would have to have a custom reamer ground, and that wouldn't be cheap.

Reason a plenty for a gunsmith to turn down the job.

The other factor of the bushed .308 chamber conversions was that they were not safe.
MacFarland, in his book, Modern Gunsmithing, reports several known failures.
He rates the action as only safe to 45,000 psi.

Not many gunsmiths, in todays legal climate, would bush and repair one for the 62,000 psi .308 cartridge.


rcmodel

 

[jpcampbell]

There are several smiths that specialize in restoration of military firearms you wouldn't be able to tell the new barrel from the original. It isn't that complicated to do.
From looking at the picture and the metal to wood fit the barrel doesn't look set back so a chamber insert is more likely the culprit.
I understand why you want to keep it in as original condition as possible,
I have several original Mauser's and Enfields and 1899, and 1905 Schmidt- Rubin's that I keep in original condition.

 

[toolman846]

Not to digress too far, but in reading this thread, a question I have had for some time comes to mind. Does anyone know, or is there anywhere I can find out, what the safely rated pressure range is for a K31 action? thanks.

Jim

 

[rcmodel]

See post #12 above.

I just said it was rated at 45,000 psi by a very knowledgeable old-time gunsmith.
I personally wouldn't doubt his word.

Guys like him & P.O. Ackley were blowing up mil-sups for fun & profit before most of us were born.


rcmodel

 

[bruss01]

There are several smiths that specialize in restoration of military firearms you wouldn't be able to tell the new barrel from the original. It isn't that complicated to do.

JPCampbel -

Maybe I wasn't very clear when I described the goal. The object is not for it to APPEAR to be all original parts. The goal is to retain the ACTUAL original parts. This is not to impress my gun buddies, this is to preserve something ACTUAL, REAL that is a century old, beautiful and with a bit of coaxing can be made to function again as it did originally. An "imitation" or "re-creation" just isn't the same in my mind.

Another thing that appears to be unclear from some of the responses, I am NOT attempting to get someone to chamber this rifle in .308. That is too high pressure for this action and should not be done. I AM interested in restoring the original 7.5 swiss chambering. I admit that a 7.5 chamber reamer may not be the most common tool in a gunsmith's shop, but I can't believe that no one, nowhere, has one and knows how to use it. I'm continuing to research this.

 

[fixyurgun]

Have you checked over at mauser central ? lots of mil/surp smiths hang out there. maybe they have the guy your'e looking for. jim

 

[Jim K]

First, my apology, I was thinking K31 when I said the rear sight is back near the receiver. Your rifle is a Model 11 and the barrel has NOT been set back. The other stuff I said is still valid.

SOMETHING had to be done in that chamber if the rifle fires 7.62 NATO. The 7.5x55 case is larger in diameter than the 7.62, wider at the shoulder, and 4mm longer. The 7.62 will load and might fire (if the extractor catches it), but the case will expand, the neck will be very short, and you could even get a case split. I think you would have remembered that.

So, again, I am back to the chamber insert or some kind of new chamber. I suspect the chamber insert, as being the easiest and cheapest.

So what now? First, get a chamber cast. You can get Cerrosafe and directions from Brownells. The cast may show you what is in there. Then see if you can find anyone with a borescope to take a good look at what you have. With that, you can at least have enough information to make a decision.

If there is a chamber insert, MAYBE it can be removed using something like a tap threaded in to the insert. If the chamber is still OK, you are back to 7.5x55 with no sweat. If not, maybe the chamber can be polished out, but watch doing that, as you don't want to make the front of the chamber larger than the rear; not a good way to get easy extraction!

Jim

 

[gamachinist]

Is it marked 308 Win or 7.62 Nato on the barrel?
Could it have been rechambered in 30-06 (7.62x63mm) instead?

In the 1960's,30-06 was probably more popular than 308 Win.It was in the 1970's when I started shooting.

 

[Jim K]

Bruss01 says the rifle is currently in .308/7.62 NATO, so it isn't .30-'06. Besides, it would be a lot of trouble to rework that rifle to .30-'06; it is not a Mauser 98, it is a Swiss Model 11, a whole different beast.

Jim

 

[bruss01]

Ok guys...

I got the rifle back from the shop (they did nothing other than look at it and diagnose "excessive headspace"). Upon close examination under strong lighting, there appears to be a chamber insert of some type as evidenced by the fact that there is a small "ring" when the mouth of the chamber is examined. This is consistent with the fact that it appears the barrel was not set back (related to me by some Swiss rifle collectors who saw a photo). I took a chamber casting which revealed nothing of interest except to confirm that it is a .308 chamber and not a 7.5 Swiss.

I've been told that either it is a thin shell type of insert (such as was used in the notorious Garand conversions), or possibly the barrel was reamed out to accomodate a more cylindrical type of insert. What I am looking for right now is somewhere to send it where they can remove whatever type of insert is in there now, and restore the original 7.5 Swiss chamber - if that involves fabricating a NEW cylindrical insert with a 7.5 Swiss chamber, then so be it.

Does anyone know of anyone who might be willing to take this on as a project? I need someone who is capable of more than just trigger jobs and replacing a barrel, someone with real machinist skills.

 

[mejeepnut]

Well the barrel will have to be pulled from the action and even tho I have a K-31 I have no idea whats needed for tools for that but a gunsmith should be able to do it no problem.If the same gunsmith does not want to go any farther for you then an actual machine shop will!They should be abe to put the barrel in a lathe and bore the liner out and if you give them the specs for a 7.5X55 swiss chamber they could most likely make an insert.Now if they could remove the liner and thread whats left of the chamber and make a carbon steel threaded insert and then once the new insert is installed then chamber ream it you would be golden I think.If all this machine work costs so much and you can't find the proper reamer and can't afford to have one made then it could be turned into any 7.62 round that you wanted.like 308 again or 30-06 or even 30-30 or 30 rem.(I can't belive I suggested the last 2).You may need to check out the face of the bolt to see if it has been altered for 308 but it is most likely fine.

 

[rcmodel]

308 again or 30-06 or even 30-30 or 30 rem.(I can't believe I suggested the last 2

The 30-06 is too long for the action, and the .308 is considered to have too much pressure for the action according to established gunsmithing experts.

I would question the integrity of a threaded insert in a high-power rifle chamber anyway. Any reputable gunsmith would decline the job on safety reasons alone.
The insert in question was to shorten the chamber from the front, not to replace old chamber and re-chamber it.

Generally the only time a chamber is sleeved and re-chambered is on low pressure calibers such as the 25-20, 32-20, 38-40, etc when the barrel is re-lined.
Nobody relines or sleeves high-pressure rifle barrels or chambers.


rcmodel