Re-Barreling/Re-Chambering my K31 Swiss

[Artful]

Out of curiosity what was the quoted price on the SS barrel blank from Shilen?

[HollowPoint]

It was just over three hundred dollars according to the gal on the phone. I could have special ordered this same barrel through midwayusa for a slight discount but not enough to make any difference as far as my budget for this project.

The standard No.4 profile chrome moly 1 in 8 twist barrel runs around $175.00 if you get it during one of their free-shipping campaigns. Even with the additional purchase of that short length of 4140 round stock the total price for the barrel will be below a couple of hundred bucks.

HollowPoint

[HollowPoint]

I had a light day of work today so I went ahead and Powder Coated all the small parts that would have otherwise had to have been re-blued. I decided to go with a flat-black finish instead of re-bluing. It didn't take to long and everything turned out looking pretty good. While I was at it I also sanded down the wooden stock and wiped it with a lighter stain than it formerly had. I still have to apply some clear over the top of it. I just want to wait till it's had a chance for the stain to dry completely. I'm wondering if I can forego the clear coat and just apply some paste wax on the finish. I'm not all that knowledgeable in the realm of wood finishes so I'll have to do some research before I proceed.

I know I'm getting ahead of myself but free time doesn't come as easily for me as it once did; and since all I was doing was waiting for my recently ordered barrel and metal stock to arrive, I thought I'd use that time to do the stuff that I would have had to do eventually anyway.

I haven't decided how I'll go about coating the barrel itself. My little powder-coating/toaster-oven isn't nearly big enough to fit my barrel into for curing a layer of powder coat. I'll think of something. I may just cold-blue it and then spray a couple layers of flat black paint over that.

HollowPoint

[HollowPoint]

My new barrel and my chunk of 4140 metal stock showed up late yesterday afternoon. I was able to set it up on the lathe and at least start shaping the outside diameters and threads. I got a real nice-snug slop-free fit on the threads and interior flats surfaces. I turned the outside shape slightly different than the factory tenon. That "difference" was in the form of eliminating the thread-relief-cuts so as to increase the support-strength of the overall length of this part.

I got as far as finishing up the outside geometry and threads of my threaded-barrel-stub. Because of this "Plan-B" method of installation, I've been pondering the optimum thread pitch I should use for mating the barrel tenon itself to the inside threads of the threaded-barrel-stub.

I don't want to use a thread pitch as course as the metric 2.0mm threads that the factory K31 barrel was screwed into the receiver with. That would give me too-course of a thread setup above and below and possibly compromise the strength of the threaded-barrel-stub; not to mention it would make the walls of my chamber just a tad thinner than I'd like. After checking around the internet for the various thread pitches used in other rifles with calibers equal to or greater than the 6.5x55 Swede, I've decided to use a one-in-14 thread pitch for mating my new barrel to the threaded-barrel-stub.

I went back and forth between a 1 in 16 and a 1 in 14 thread pitch for the same reason. The factory tenon only has about an inch of total threads from front to back on the existing tenon. I can see why they used such a course thread pitch. It most likely gave a more secure hold than a one inch length of finer threads.

With this threaded-barrel-stub setup I have about a 2-1/4" length of overall threads so going with a little finer thread pitch should still secure my new barrel without issue; and, as I've already mentioned, it will allow me to keep the walls of my barrel chamber and the walls of the threaded-barrel-stub as thick as possible; given this setup.

I know it's hard to visualize with just the written word being used to paint a mental picture. I'm afraid that what I'm writing won't make any sense until I post some of the pictures I've taken. I'm hoping to have this threaded-barrel-stub done tomorrow. I still have to bore out the "Minor-Diameter" hole that I'll be cutting my inside diameter threads into. After that I can remove the newly turned part from my metal stock and proceed to index, mark and then cut the angled extraction-cam and extraction-notch.

I'll be back after I've finished this part and edited some of the photos I've taken.
HollowPoint

[Artful]

I haven't decided how I'll go about coating the barrel itself. My little powder-coating/toaster-oven isn't nearly big enough to fit my barrel into for curing a layer of powder coat. I'll think of something. I may just cold-blue it and then spray a couple layers of flat black paint over that.

HollowPoint

I read of some using a section of 36" long stainless steel double wall fireplace chimney pipe with a hot plate in the bottom,
a lid with a damper on top, and a BBQ grill thermometer to watch the temp.
Loose brick base for the hot plate to set in, and the pipe to set on top of.

Another was the aluminized insulated board formed into a long box which opened from the top and he mounted heat lamps about every foot or so and controlled it with a dimmer switch and had two probe digital thermometers with alarms to monitor the contents.

Here's a quote from Mac's Shooting Irons http://www.shootiniron.com

Any metal cabinet will work as long as you insulate it. Drywall works fairly well for that. You can also use cheap tile layed in the bottom as a heat refelctor. I built a "hot box" for heating the parts getting Guncoated using ceramic tile in the bottom as heat reflector for the heating coils and insulated it with dry wall.

I've been using that thing for years and it works very well. The one thing that I would add: If you do a lot of curing, don't waste time with mechanical thermostats. Spend the few extra dollars and get an electronic heat controller. You can get them on Ebay for less than $20. (Watlow, Omega, etc)

Those will ramp the heat up in stages instead of just "flame on".

Regarding fans: Excellent suggestion! My big curing oven has a metal bladed fan that extends thru the top on a long shaft. It blows the air around inside the oven like a whirlwind and keeps the temp even throughout. Keep yer powder dry, Mac.

Lots of You Tube plans to make a curing oven

https://www.youtube.com/watch?v=NeRSp-YBIpE

https://www.youtube.com/watch?v=81t1aYxJer0

Other links

http://www.stickbow.com/features/bow...ng/heatbox.CFM

http://www272.pair.com/stevewag/heater/heater1.html

[Cap'n Morgan]

Since you'll be doing all threading on a lathe, you could go for any thread profile you want. Instead of full profile threads you could use a thread with flat root and crest, thereby making the thread profile lower for the same pitch. The "pointy" parts of a thread adds very little to the actually strength and 0.02-0.03" is plenty of height for a 1 in 14 thread. Also you could change the compounded angle profil from 55 or 60 degree to 30 as this (theoretical) would lessen the radial outward pressure on the barrel stub.

[HollowPoint]

I read of some using a section of 36" long stainless steel double wall fireplace chimney pipe with a hot plate in the bottom,
a lid with a damper on top, and a BBQ grill thermometer to watch the temp.
Loose brick base for the hot plate to set in, and the pipe to set on top of.

Another was the aluminized insulated board formed into a long box which opened from the top and he mounted heat lamps about every foot or so and controlled it with a dimmer switch and had two probe digital thermometers with alarms to monitor the contents.

Here's a quote from Mac's Shooting Irons http://www.shootiniron.com


Lots of You Tube plans to make a curing oven

https://www.youtube.com/watch?v=NeRSp-YBIpE

https://www.youtube.com/watch?v=81t1aYxJer0

Other links

http://www.stickbow.com/features/bow...ng/heatbox.CFM

http://www272.pair.com/stevewag/heater/heater1.html

I was mulling this over last night and I thought maybe I could insulate the door area of my tiny little toaster oven so as to powder coat the rear half of my barrel -stuck into my oven at an angle from corner to corner- then turn it around and do the other half.

Of course, this would still leave a short section in the middle of my barrel's overall length that wasn't powder coated. That center section is hidden underneath the forestock so from an asthetic point of view, it may not be an issue. That center section can just be cold blued and painted.

This is a budget project. Nearly everything I've done to this rifle thus far has been by using stuff I already had on hand; either in my junk drawers or out back in my junk pile. The stain for the stock, the urethane for the finish, the cold blue; should I need to use it, the flat black powder coat; all of that stuff I just happened to have on hand already.

The only thing I've had to buy or have already bought are the barrel, the reamer, and the range rod. The 4140 metal stock I bought using the spending money I had in my paypal account so I really don't count that as an expense; per se.

I'm trying to avoid spending any more money than I have to on this project. I have a friend/customer who has a powder coating oven large enough to do a 26" barrel if I set it in there from corner to corner. Since both ends of my barrel will be threaded, I might be able to just lean it inside the oven. That's if he's open to loaning it to me.

HollowPoint

[HollowPoint]

Since you'll be doing all threading on a lathe, you could go for any thread profile you want. Instead of full profile threads you could use a thread with flat root and crest, thereby making the thread profile lower for the same pitch. The "pointy" parts of a thread adds very little to the actually strength and 0.02-0.03" is plenty of height for a 1 in 14 thread. Also you could change the compounded angle profil from 55 or 60 degree to 30 as this (theoretical) would lessen the radial outward pressure on the barrel stub.

I get the just of what you're saying; and it makes sense. Actually, I had already planned on using 1 in 14 pitch thread without going to their full profile; for all the reasons you've just stated. The thing is, when I cut these threads as "Class-3A" and "Class-3B" threads, it makes an already tricky procedure even trickier for me. I mentioned before, "I'm neither a gunsmith nor a machinist." Cutting full profile "Class-3" threads is tricky enough for me as it is. Cutting these same "Class-3" threads and intentionally giving them flat tops and bottoms adds a little more complexity for me.

I think that as long as the threads themselves mesh perfectly together as should be the case with "Class-3" threads, the thickness of the chamber walls and the thickness of the threaded-barrel-stub walls (within reason) shouldn't be a problem. If the threads fit snuggly together, there will be no microscopic gaps large enough for the metal to creep into and out of shape under the pressure and heat that's experienced with repeated discharging of cartridges; I hope.

If I start to get the sense that my deliberately flattened thread tops and bottoms don't look like I'm hoping they will, I can just keep cutting them to their full profile and go with that. No harm, no foul.

I found the following website that has been a big help with calculating the nuances of all the various thread pitches. It's alot cheaper than buying a Machinist Handbook. I just wish I could find a similar website that would help with metric threads.

http://theoreticalmachinist.com/Thre...dImperial.aspx

HollowPoint

[Cap'n Morgan]

I found the following website that has been a big help with calculating the nuances of all the various thread pitches. It's alot cheaper than buying a Machinist Handbook. I just wish I could find a similar website that would help with metric threads.

http://theoreticalmachinist.com/Thre...dImperial.aspx

You can try this one. It's in German, but Google translate is your friend. Unfortunately it doesn't allow for thread gauge wire calculation:

http://www.iso-gewinde.at/

Or you could try the program "threadTech" It's a great program as it will allow for any thread gauge wire size you may want, but it's probably overkill unless you make threads for a living. You can download a 30 days trail version here:

http://www.threadcheck.com/content/s...e_download.asp


Metric thread tolerances are based on the ISO system and can be a bit daunting at first look, but it makes good sense once you get the hang of it.

http://www.boltscience.com/pages/screw8.htm

[HollowPoint]

Here are a few more pics with some explanatory text superimposed onto them. Hopefully they'll clarify some of what I was attempting to describe in my previous post.

I still have to mark and cut the Extraction-Notch as well as the Angled-Extraction-Cam and a small flat on the bottom of my threaded stub. I'll post pics of that after I get those operations done.

HollowPoint

[Plate plinker]

I don't know much at all about this process but you seem to getting on well for a home gunsmith.

[HollowPoint]

I assure you, it only looks that way. Since I've never worked on a K31 before there still exists a certain sense of trepidation about it. In the back of my mind are all of those comments I came across during my research into this K31 re-barreling project. ("The Angles Are To Complex, It's Not Worth The Trouble, There's only a few guys in the world that know how to work on these rifles, It's going to be real expensive." And of course, there's the replies of the purists; "Why Would You Want To Bubba Such A Fine Rifle?")

When you add all of those negatives to my own sense of trepidation; Like, Did I cut the threads with enough precision? Are my measurements tight enough to ensure safety and reliability? Is there anything I've forgotten to do or to check? After all of this work and money spent, will it be blown to smithereans when I go to proof test it?

On the other hand, if I end up with the kind of rifle I've dreamed of building, I'm afraid that I'm going to be a Cocky-SOB for a short period of time shortly there after but, I'll get over that soon enough. From then on, any time I come across a Dream-Killing remark about a K31 re-barreling project, I'll be able to hold my own against the self-appointed-experts. Having successfully completed this K31 re-barreling/re-chambering project, any similar projects on just about any other type of bolt action rifle will seem immensely doable by comparison.

HollowPoint

[ratboy]

When you add all of those negatives to my own sense of trepidation; Like, Did I cut the threads with enough precision? Are my measurements tight enough to ensure safety and reliability? Is there anything I've forgotten to do or to check? After all of this work and money spent, will it be blown to smithereans when I go to proof test it?
HollowPoint

imagine what the guys who built the apollo rocket were thinking when they saw it headed to the launch pad.

from what ive seen so far, i expect a positive outcome. problem is once this works, you will start coming up with other "projects"

[Artful]

I was mulling this over last night and I thought maybe I could insulate the door area of my tiny little toaster oven so as to powder coat the rear half of my barrel -stuck into my oven at an angle from corner to corner- then turn it around and do the other half.

Of course, this would still leave a short section in the middle of my barrel's overall length that wasn't powder coated. That center section is hidden underneath the forestock so from an asthetic point of view, it may not be an issue. That center section can just be cold blued and painted.

This is a budget project. Nearly everything I've done to this rifle thus far has been by using stuff I already had on hand; either in my junk drawers or out back in my junk pile. The stain for the stock, the urethane for the finish, the cold blue; should I need to use it, the flat black powder coat; all of that stuff I just happened to have on hand already.

I'm trying to avoid spending any more money than I have to on this project. I have a friend/customer who has a powder coating oven large enough to do a 26" barrel if I set it in there from corner to corner. Since both ends of my barrel will be threaded, I might be able to just lean it inside the oven. That's if he's open to loaning it to me.

HollowPoint

If he doesn't what else you got around - heck two layers of drywall is a firewall rate for 1 hour against open flame - build your bake box/flue out of that - do it horizontally and put the toaster oven on one end with door removed and a flue with a fan to move the hot air down the box - on the other end put a flapper that's controllable - steal the thermometer from your BBQ to make sure the temps up to spec's. This ain't rocket science.

Heat Source + container to hold the heat and the part + way to measure the temp and control the temp - That's it

[HollowPoint]

imagine what the guys who built the apollo rocket were thinking when they saw it headed to the launch pad.

from what ive seen so far, i expect a positive outcome. problem is once this works, you will start coming up with other "projects"

"Once It Works"

Yea; I've found that like other projects I've done, no sooner do I get near the end of my project that I figure out ways I could have done it better or easier. From that learning process comes those "Other Project" you elude to. I agree with you.

In the back of my mind I have thoughts of re-barreling my Lee Enfield No.4 yet again. This time around I'd true-up that receiver as well and go with a 1 in 14 twist barrel instead of the 1 in 10 that I used before. Since it's my dedicated lead plinker, a slower twist would be ideal for me.

On a subject related note: I got the Threaded-Barrel-Stub done yesterday. I thought I had every measurement checked and re-checked for a perfect fit. I torked it into place with high hopes of the action working perfectly the first time with no do-overs. NOT. With the Threaded-Barrel-Stub in place, I couldn't get the bolt to go into battery. It would stop short of going all the way in.

I thought to myself, WhatTheHell! All my Barrel-Stub measurements were right on the money. Why is this not working? Then I remembered that when I squared up the face of my receiver I had taken off about three and a half thousands of metal. This meant that when I torked down my Threaded-Barrel-Stub into the receiver, it was seated a good five-thousands or so deeper than it was intended. Hence the failure to go into battery. In my hurry to finish the Threaded-Barrel-Stub, I failed to take that into account. It's an easy but annoying fix. Better to have three-and-a-half-thousands of metal to be removed than to come up short and have to start from scratch. It was then that I ran out of free time.

I have some more free time near the end of the week. I can get those bugs ironed out then and move on to ordering my Range-Rod for the next step in this project. I'll be setting my new barrel up on the lathe for doing both the indexing and the threading of the tenon and muzzle.

HollowPoint

[HollowPoint]

I finally got it done and re-tested. My bolt now goes into battery as it should with just a hint of contact between the right-side Bolt-Lug and the Angled-Extraction-Cam on the face of the Threaded-Stub.

I'll have to wait till I have the new barrel installed in order to fully test the actual extraction of the empty shells. I'm confident it will work though.

Although going to "Plan-B" has added some extra work to the front end of this project, I do think that in the long run it will save me some time when it comes to head-spacing. In theory, I should now be able to just cut my chamber so that my 6.5x55 brass sits at that same depth as an empty 7.5x55 casing fits into the factory barrel chamber. From there it's just a matter of removing the extraction claw from the bolt and screwing the new barrel down till it touches the bolt-face. (with a go-gauge in place of course) Then I can tork down the Barrel-Nut and proof-test it. Lets hope it works out so easily.

Here are a few of the pics of what I went through in order to get it to work. I hope they make sense to you all. If not, you're allowed to ask questions.

HollowPoint

[Cap'n Morgan]

That's neat! The idea of using a template and file never crossed my mind. Too many years of CNC I guess...

Is the original cam hardened in any way?

[McFred]

Thank you HollowPoint for this thread. I remember years ago when I stumbled onto the K31 straight pull milsurp rifle. It piqued my curiosity but I never followed up on it. Now I'm shopping for one I can reverse-ably sporterize for a 284Win scout rifle I can take to the local rifle matches to badger the local tacticool and F-class guys. (I'm heavily invested in high BC 7mm components).

Along those lines what is the max cartridge overall length the magazine supports (if I may ask)?

Really looking forward to the range report!

[HollowPoint]

That's neat! The idea of using a template and file never crossed my mind. Too many years of CNC I guess...

Is the original cam hardened in any way?

I don't know if it's hardened or not. When I was filing my templates; as I held them pressed against the factory tenon, the file had no problem scoring the finish of the factory Angled-Extraction-Cam so I'm thinking; if it was originally hardened the repeated extreme heating and then cooling of the chamber area of the factory barrel had long since annealed to its original neutral state of hardness. There's no way I can prove it though.

I think that at a minimum, the level of hardness of the factory tenon area as it exists right now and the hardness of the 4140 alloy metal stock I used to make the Threaded-Barrel-Stub are pretty close to the same; with the 4140 being the newer un-fatigued metal.

I'll have to measure the length of the inside of my K31's magazine in order to answer the "Max overall length of the cartridge" question. Right now I have to go to work. I'll post an answer this afternoon.

HollowPoint

[Cap'n Morgan]

Hollowpoint.

The reason I'm asking is that back in the day actions and bolts were often hardened to different hardness in different areas. A cam, like the one on your barrel, could have been flame hardened for wear resistance without the process interfering with the rest of the chamber. Anyway, a smidgen of molycote based grease should prevent any galling.