Gunsmithing K31 rebarrel in 7.5 x 55 Swiss information.

[lrgrendel]

I have a K31 barreled action with a worn out and pitted bore.
Looking for experienced information on the above caliber.

Would like to do maybe a heavy barrel with a bench rest type stock. I own three K31’s so I really like the bolt system and action!
Have these been re- barreled before? Are there reamers available?

Thanks

 

[Davester]

Yes and yes. However a peculiarity of the design is that there is a cam on the breech face to close the bolt. Loads of information on this at Swissrifles.com.

I have heard of smiths using the tenon from the old barrel as a stub and fitting a new barrel to that, but not what you want if your aim is bench-rest. Of course in Switzerland, when your K31 wears out, you just buy another as that is much cheaper.

If you re-barrel you may consider changing calibre to 7.62x51 as it is ballistically pretty much identical and ammunition/components will be easier to come by.

 

[lrgrendel]

Thanks for reply.
I was just reading the forum on Swissrifles!!

Yes. This is not going to be a K31. Don’t even have any of the wood or components.
Want to keep it 7.55 x 55. I already reload for it and don’t want to have to mess with the bolt face or magazine.

 

[Wannashootit]

My understanding is fuhgeddaboutit.
The breech surfaces of the K-31 barrel are so complex and difficult to machine that I've read they utilize the old barrel stub bored-out and sleeved over the new barrel.

No clue how it's done, or even if you can find a smith with the experience to do the deed- but I'd be curious to know exactly how it's done (and what it cost$$) should you find out.

I do remember when I started handloading for mine (hasn't been outta the safe in forever) that the published OAL for the 7.5 x 55 was way outta whack for the K-31, which seemed to have much less freebore than the "book"- which is apparently based on the older rifles like the K-11.
I'm sure if you are able to find a smith that does this work he'll be knowledgeable on reamer specs.

 

[fdkay]

I would love to build a precision rifle in 7.5. GP 11 is the bomb.

 

[Ledzep]

Might check with some of the smiths that have 4 and 5 axis machines (Area 419 comes to mind). Could probably manage that breech face geometry if they're willing.

 

[lrgrendel]

Tried Area419. They are not interested.
Still looking thanks.

 

[Ledzep]

Well you can ask LRI but chad likes to send all the customers that call and ask about Savage work over to Travis Stevens so Idk how you'll fare asking about a K31.

 

[mcfred]

This is an old thread where the OP rebarreled his K31 to 6.5x55. The breech face cam geometry didn't look all that hard to me, especially if you have a working example as a template. If you can cut a Win M70 extractor claw slot in a barrel tenon then you can do the K31. It just not easy and fast unless it's something you do routinely. You'd be surprised what you can accomplish with patience and a file.

Re-Barreling/Re-Chambering my K31 Swiss

It's been a long time coming. I've dreamed of doing this since bringing this rifle home. Why? There are many reason I can come up with but, to anyone asking "Why," no reason is good enough. Lets just say I'm tweaking an already very-good rifle to my own preferences. On Wednesday I had...

castboolits.gunloads.com

Sorry, most of the pics are dead now.

 

[lrgrendel]

This is an old thread where the OP rebarreled his K31 to 6.5x55. The breech face cam geometry didn't look all that hard to me, especially if you have a working example as a template. If you can cut a Win M70 extractor claw slot in a barrel tenon then you can do the K31. It just not easy and fast unless it's something you do routinely. You'd be surprised what you can accomplish with patience and a file.

Re-Barreling/Re-Chambering my K31 Swiss

It's been a long time coming. I've dreamed of doing this since bringing this rifle home. Why? There are many reason I can come up with but, to anyone asking "Why," no reason is good enough. Lets just say I'm tweaking an already very-good rifle to my own preferences. On Wednesday I had...

castboolits.gunloads.com

Sorry, most of the pics are dead now.

This is the most helpful information I have received yet, thank you very much.

I am not a gunsmith but I read somewhere that the barrel needs to be chambered before the complex work is down at the breech end of the barrel?
I guess reverse from the normal way of doing it? Don’t understand way.

I will keep you informed.

 

[ptosis]

Just stumbled on this old post; wondering if you had any luck rebarreling our favourite carbine in these past few months.

(First, a disclaimer: I never did rebarrel a 31, as when one's word out, I just pick another.)

This said, the main problem is not so much machining the cam at the receiver end of the barrel. This is exotic, but not overly complex; if it is of any interest, I think I can find a copy of the original Waffenfabrik blueprints of the part.

The main problem is headspace. If I remember it correctly, the correct headspace on the original K31s was established at the factory by fitting the right bolt face; there were 3 different ones, with 0.05 mm step.

Hence, the approach described by Wannashootit above: the barrel is cut to leave only a stub (incl. the machined cam), then the stub is drilled, and an internal thread is cut in it. The stub is then used as a holder to screw in a new barrel (and the headspace is established the usual way). That is how the only successful K31 rebarreling I've seen was done.

Hope this helps.

 

[fdkay]

Just stumbled on this old post; wondering if you had any luck rebarreling our favourite carbine in these past few months.

(First, a disclaimer: I never did rebarrel a 31, as when one's word out, I just pick another.)

This said, the main problem is not so much machining the cam at the receiver end of the barrel. This is exotic, but not overly complex; if it is of any interest, I think I can find a copy of the original Waffenfabrik blueprints of the part.

The main problem is headspace. If I remember it correctly, the correct headspace on the original K31s was established at the factory by fitting the right bolt face; there were 3 different ones, with 0.05 mm step.

Hence, the approach described by Wannashootit above: the barrel is cut to leave only a stub (incl. the machined cam), then the stub is drilled, and an internal thread is cut in it. The stub is then used as a holder to screw in a new barrel (and the headspace is established the usual way). That is how the only successful K31 rebarreling I've seen was done.

Hope this helps.

Seems to me, you could use a pull through reamer, like they use on the garand and M14

 

[ptosis]

Seems to me, you could use a pull through reamer, like they use on the garand and M14

Yes! That's a great point, thanks!

 

[Davo308]

I read over on swiss rifles that the smith for this had passed a few years back.

 

[ptosis]

Found the drawings, for those who care. Original Waffenfabrik specs:

Enjoy.

 

[mcfred]

Thanks for the tenon/barrel print. It's nice to see technical drawings like that.

 

[Wannashootit]

Leave it to the Swiss, eh? Nothing simple about that breech.

 

[Ledzep]

Found the drawings, for those who care. Original Waffenfabrik specs:View attachment 7475053
Enjoy.

One of the coolest things I've seen posted on this forum. Got any more?

Thanks for sharing!

 

[Ledzep]

Couldn't help myself... Today's lunch project. I'll likely make and post an "updated" PDF print when I get around to it. That helical cut on the breech face is going to take a 4th axis machine and a 7 degree profile tool but should not be impossible.

 

[fdkay]

So, how did they do that shit before the advent of CNC and keep any type of reasonable tolerances?

 

[Ledzep]

Give-a-shit, knowledge, and skill.

There was probably a specific machine who's only purpose was to cut that helical feature. The cut opposite the extractor relief also can't be cut with a CNC (or manual for that matter) mill and requires a shaper, chisel, file, etc.. to get square corners in the bottom.

 

[LeftyJason]

So, how did they do that shit before the advent of CNC and keep any type of reasonable tolerances?

They did use cam type tracer machines once upon a time. They would have one machine set up for just that cut and all of the other specialty cuts.

Give-a-shit, knowledge, and skill.

There was probably a specific machine who's only purpose was to cut that helical feature. The cut opposite the extractor relief also can't be cut with a CNC (or manual for that matter) mill and requires a shaper, chisel, file, etc.. to get square corners in the bottom.

It is possible to broach on a cnc or manual mill. It might take some crazier fixturing to cut it but it is possible. There are videos of people doing it on YouTube. Depending on geometry the cut could be done with a slitting saw. Can't see it that well.

Ps. There is possibly some archival footage out there somewhere for something like that out there but my interblag fu can't seem to find any. If anybody can find any that'd be great.

 

[Wannashootit]

I'm about ready to go dig mine out of the safe...
In looking at the original drawing, the area of the shoulder ahead of the tenon relief cut is odd- as in asymmetrical top and bottom (doesn't show that way on the rendering).
WTF is that? Not possible to turn that feature.

 

[Ledzep]

Looks like a flat for torqueing the barrel on.

PDF in imperial format.

 

[LeftyJason]

Looks like a flat for torqueing the barrel on.

PDF in imperial format.

What is the shape of the 0.138 groove at the base of the helical cut? Cross section through it like you have one through the 0.256 groove?

 

[Ledzep]

The original shows it better, appears to be rectangular and about 2mm deep but I don't see a specific depth call-out. I'll check my K31 when I get home

 

[mcfred]

Ledzep, look like that that 7˚ helical face for the extraction cam might not have made it into production(?). Here are a few tenon pics stolen from the internet, at least one of which is Guisan's. The cam looks flat. While I can't find any photos of the bolt sleeve lugs, I can 't remember a corresponding 7˚ feature it would articulate with:

Seeing that print in imperial units churns my guts; just a reaction, not a judgement.

 

[LeftyJason]

Ledzep, look like that that 7˚ helical face for the extraction cam might not have made it into production(?). Here are a few tenon pics stolen from the internet, at least one of which is Guisan's. The cam looks flat. While I can't find any photos of the bolt sleeve lugs, I can 't remember a corresponding 7˚ feature it would articulate with:


View attachment 7481474View attachment 7481475
View attachment 7481473


Seeing that print in imperial units churns my guts; just a reaction, not a judgement.

Considering most here don't have access to metric machines or gages it makes sense.

 

[mcfred]

I know. It just looks wrong. Like a BMW M3 with a pushrod 2V 350SB Chevy. Maybe a better analogy is seeing a Howa barrel tenon spec-ed as Ø1.027"-16.93 TPI instead of M26x1.5. Both ways will get the job done.

 

[Ledzep]

Ahh! It's a circular cut! I see it on the print. Can't quite make out the diameter 4mm I think.

 

[lariat]

Give-a-shit, knowledge, and skill.

There was probably a specific machine who's only purpose was to cut that helical feature. The cut opposite the extractor relief also can't be cut with a CNC (or manual for that matter) mill and requires a shaper, chisel, file, etc.. to get square corners in the bottom.

Should be able to do it with a lathe that has live tooling. That would hold an endmill in the right position to make the corner. unless I am looking at the wrong feature. A horizontal mill might be able to do it but the fixture would be a nightmare.

 

[Clark]

I paid $80 for a K-31 with a bore that looks unfired.... the stocks look used. Crazy names under the butt plates.

I shot one in 2014
7.5mm Swiss, K-31, 284 brass sized with Lee die, CCI200

1) 168 gr Sierra .308 Match King

a) 42 gr IMR4895 ok, kinda wimpy
b) 45.5 gr IMR4895, ok, primer starting too flatten, 4" group open
sights

 

[Ledzep]

Ledzep, look like that that 7˚ helical face for the extraction cam might not have made it into production(?). Here are a few tenon pics stolen from the internet, at least one of which is Guisan's. The cam looks flat. While I can't find any photos of the bolt sleeve lugs, I can 't remember a corresponding 7˚ feature it would articulate with:


View attachment 7481474View attachment 7481475
View attachment 7481473


Seeing that print in imperial units churns my guts; just a reaction, not a judgement.

It's very subtle looking, even in my rendering. I think it's there in those pictures, too. The print has revisions through the early/mid 30's; well into production so I very much doubt that the feature was left off.

 

[Davo308]

View attachment 7482179

I paid $80 for a K-31 with a bore that looks unfired.... the stocks look used. Crazy names under the butt plates.

I shot one in 2014
7.5mm Swiss, K-31, 284 brass sized with Lee die, CCI200

1) 168 gr Sierra .308 Match King

a) 42 gr IMR4895 ok, kinda wimpy
b) 45.5 gr IMR4895, ok, primer starting too flatten, 4" group open
sights

They are great rifles. I've got a pair, one scoped with a brake the other au natural.

I picked up a case of GP11 but no local ranges allow it.

Im hoping to reload for it and on paper, my scoped rifle should get to 800 yards here...

 

[lrgrendel]

Here is where I am.
The first trial was cut in aluminum and came out perfect.
I have a 30” barrel on order from Krieger. It will be another 4 months!

I want to do a Bench Rest/F-Class type of stock. Having trouble finding someone.

Thanks for those drawings. They will be extremely helpful.

 

[Wannashootit]

I see Richards has stocks for it, but nothing in a BR style.
Might be worth a call anyway, given that they have the inletting program would seem to be something they could do.

 

[lariat]

Here is where I am.
The first trial was cut in aluminum and came out perfect.
I have a 30” barrel on order from Krieger. It will be another 4 months!

I want to do a Bench Rest/F-Class type of stock. Having trouble finding someone.

Thanks for those drawings. They will be extremely helpful.View attachment 7483940View attachment 7483941View attachment 7483942View attachment 7483943

Curious about how you did it. 90% of machining is problem solving and I’m always interested in how others think and attack the work.

 

[lrgrendel]

I see Richards has stocks for it, but nothing in a BR style.
Might be worth a call anyway, given that they have the inletting program would seem to be something they could do.

I actually have one of these. We are fitting it right now for a different project.

 

[lrgrendel]

I didn’t do it. 2 friends did.
It was done on a regular CNC machine.

 

[Blastattack]

Found the drawings, for those who care. Original Waffenfabrik specs:View attachment 7475053
Enjoy.

I realize this is an old thread, but do you have any more prints? I see a stack behind this one.