My first post, and its a question regarding barrel tenon bushings!

[corerftech]

Im a new member here on the forum. This is my first post of any kind, and I am posing a question to the gurus.

Im a third semester machine school student, but deeply middle aged and an electrical contractor. I will add, I am level 3, not in my third try to pass level 1. Im not on the 14 year plan for a certificate.

Bottom line is gunsmithing has called me for many years and I finally have tried to answer the call with at least some education and proper tooling.

I have a bunch of projects, most are straightforward. This one is GOOFY.

This is regarding a 74/95 Swede Rolling Block in 8x58. Rifle is immaculate, but I refuse to buy brass, dies, etc for the RD cartridge. I would rather burn the stock in the fireplace and use the barrel as a tomatoe stake.
I have contemplated for many months what to do. Big case head, very few parents and those that can donate brass, are just as overpriced and odd/rare. 32-348 Win, etc.
I will add this, yes Im going to alter the old rifle. Someone else can preserve for all humanity, another one. Mine will be shot, very well, with ammo I can handload with ease and accuracy.

So looking at the barrel and chamber cast, I have found at least one solution if not two. Not sure which one is better, one will look prettier for sure after some bluing. I'd like to not refit the barrel but I really have no choice. I like the sights, the finish, etc. 29 inch barrel will serve very well for another 32/8mm cartridge, well it may only be 27 inch when Im done but still, an awesome bunny rifle it could be.

Setting the barrel back is a 1.7 inch SETBACK! There is a knoxform octagon section at the receiver which has a lug for forend retention milled into the lower section.
My thoughts are as follows:

PLAN A-

Set barrel back 1.8 inch. Turn the old barrel shank, thread and fit. Bottom line is I will leave as much barrel shank as I can and still clean up for a 32-40 chamber.
This will end up removing any hope of a shoulder that is formed by the barrel. I will need to make a Savage type barrel nut, but will fit the nut and dimension so that it resembles the old knoxform octagon to fill the gap in the forend. Mostly cosmetic, but also setting of headspace reference. Also allows me to time the sights back to TDC.
The forend will need to have some adjustment (shorten).
I will need to fab a small tab to tig onto the bottom of the new barrel nut to act as a tab for the forend attachment.

So far have I overlooked something as far as dimensions, heat treatment loss, wall thickness, etc? The neck of the cartridge will be in a barrel diameter of about .75-.80 when finished. Although hidden under a barrel nut, the nut wont really add meat to the barrel. Just a shoulder.
Id be using 4140 (grey on the alloy chart) annealed for the nut and forend tab. Thats what I have on hand. IS THIS BAD material to use??

PLAN B-

Set barrel back even further. Basically lop off the back end a solid 2.25 inch. This leaves me a fresh barrel stub. That stub will be approx .800 diameter for a good 2 inch. Think end of a Martini Cadet barrel shank dimensions.
I now have a small OD barrel blank to work with.
Use same GREY 4140 alloy, bore and thread to .750 x 20 tpi.
Turn and thread the stub to .750x20tpi
Marry said stub barrel to the receiver bushing. Locktite as would a liner.
Bushing would be again designed to fill the void the octagon section occupied, so that the forend would have no huge gaps (cosmetic) and I'd have a nice hunk to stick in the barrel vice without fear of separating the bushing/stub.
Additionally the bushing would be the same diameter as the octagon section, which is about 1.100. Pretty fat. And its 2 inch long in front of the receiver. A 32-40 2 inch log cartridge neck would be smack in the middle of this area.

Rethread to .980 (iirc)x12tpi square and refit to action. (This would allow me to also prep the breech block and receiver face squaring both, prior to fitting, pin replacement if needed, etc)

Chuck up and chamber as usual for 32-20 (my far more desired round, this is a rabbit rifle, not a schuetzen masterpiece.) that I can push as hard as I want with a round nose for meat taking. OR back to 32-40 even.

I forgot to add, post threading the bushing, I need to cut a flat for the forend tab and tig a small tab as I mentioned above. The tab can be installed at any phase practical, so as to not heat the barrel at all AND only heat the bushing once it has been threaded and refit.

DID I MISS ANYTHING, am I asking the .750 barrel stub to support more torque/shear/pressure, etc than it can with the dimensions above? The bushing is thin but I am also not asking for 50-65kpsi. Only 25k and under with smallish bolt thrust. It will be ONLY smokeless. I'd like to take full advantage of the heat treat in 1895 and use all 20-25kpsi if desired. Id also like to preserve the pristine bore and not shoot 32-40 BPCR. 32-40 is just a bot too large for the intended purpose but then again, I am trying to reuse a barrel and sights with minimal investment or funds.

I know the martini cadet has been rechambered successfully to 32-40 many, many times and even 32 special. Albeit the receiver is mucho strong, still the barrel tenon is only .750 and the cartridge is (rounding up) .430. The chamber wall is thin. My chamber wall is just as thin with a bushing around it making it even thicker.

I know a new barrel is ideal. This is NOT a project that is for rebarrel. This is a skill building project. Its a challenge to reuse the old fine barrel, using dies/reamers/tooling already in supply here.
I just have never made a bushing for a rifle receiver and am concerned I have either made a simple bushing very complicated & dangerous or have simplified a ridiculous idea of making a bushing to preserve a barrel.

I have calculated REBORING, please dont offer as an option. Its $350 ++ to rebore/chamber and then Im probably limited to 35-348, 32-348, 38-55, etc and all will need more reloading tooling on top of that price. Rabbits, squirrels, etc at 38-55, it doesn't work for me! Id just as soon shoot 45-70 at them.

Also calc'd relining myself. $165 for liner, to preserve the front sight, two PTG piloted drills (9/16 and 7/16), turning the liner to .050 for 6 inch at muzzle to protect the front sight and preserve barrel length ($190 in drills ++)

OOOOORRRRR----

A scrap of 4140 annealed (stronger than the barrel steel is right now for sure)
Locktite
my lathe, some minor tooling
A reamer I own

El Cheapo



I appreciate any and all input. I know very little of metallurgy, or of heat treating (next classes I take). I can do the metal work successfully on the first try, but I'd also like to not destroy my RB or my face, etc.
I just cant see .980 worth of chromo/swedish junk steel and then 1018 heat treated receiver (as I understand, there is no heat treated 1018) failing at 25kpsi with a modest case head diameter (well under .500).
The question at hand is, will this bushing be employed successfully or are there hidden evil details I have overlooked like a cliff in Mexico??

I figured Id hold my first post till I really really wanted to anger other members, or make them belly laugh.

I am asking with the greatest of respect.

Thanks in advance

Mike in So Cal.

 

[RWO]

Before jumping off into cutting the barrel, why not bore out the original chamber and shrink fit a 4140 bushing that you can chamber for 32-20. Should work for such a low pressure cartridge. This preserves the original barrel exterior including tenon. You will have about .900" of freebore between the front end of the 32-20 chamber and the beginning of the rifling but handloads might eliminate any inaccuracy problem.. If it doesn't work out, you can always proceed with cutting the barrel back as necessary.

RWO

 

[Artv]

Before jumping off into cutting the barrel, why not bore out the original chamber and shrink fit a 4140 bushing that you can chamber for 32-20. Should work for such a low pressure cartridge. This preserves the original barrel exterior including tenon. You will have about .900" of freebore between the front end of the 32-20 chamber and the beginning of the rifling but handloads might eliminate any inaccuracy problem.. If it doesn't work out, you can always proceed with cutting the barrel back as necessary.

RWO

+1 on shrink fitting the bushing. The freebore will somewhat reduce the chamber pressure which will give you a little leeway in reloading smokeless.

Plan A is just basic gunsmithing, if the cosmetics are good for you, go for it.

Plan B I have a little problem with. I don't know if there is enough safety factor for smokeless powder, IF I did it that way, I would definitely run a proof load or two through it. If you restrict it to BP only, maybe a different story.

Art

 

[GGaskill]

Anything you can do to avoid having to weld 4140 will be an advantage. It is something you really don't want to do as the 4140 will get real hard from the collateral heat treating unless some pretty complicated procedures are used.

 

[sealark37]

+1 on the solution proposed by RWO. I would add Locktite. Regards, Clark

 

[corerftech]

Following up on the post:

I have chosen to NOT alter the original rolling block in such good condition. I did buy four more RB's, 3 of them in 8x58 with poorer bores. They have yet to land. When I inspect, I will choose new candidates for alteration based on poorest bore condition.

Ive decided to take the worst of them, set it all the way back and have it rebored to 35 cal.
I will likely chamber to 38 special, shorten barrel and make it a +P+ rabbit rifle. This will leave enough meat in the throat area with a low pressure round to keep a modicum of safety avail. I handgun hunt hot 38 and modest 357 mag cast SWC bullets and it does a great job of slamming them nice and hard but leaving a clean hole with no meat loss (if abdomen or head shot)
Its trajectory will not be optimal, I really wanted a lighter longer bullet with flatter flight but Ill take what I can get. I hunt my 357 out 125 yards with holdover on an 8 inch barrel. Surely less holdover and a few more FPS will be made, plus the long sight radius with a 38 special loaded hot. I should do better, more consistently. Im looking for less holdover at that distance.

I will still review another for a reline later. I will need to reduce the diameter of bore to 30 cal dimensions and likely make it a 32-40 Remington Hepburn (308) so that I can retain the entire breech section as threaded and the entire muzzle section.

I do have a question though and I admit I am a fool in this arena.

If a 4140 LINER is installed in an old barrel (its a 1 inch OD barrel with a 11/16 diameter liner at the breech), how is that acceptable and an exterior 4140 breech bushing not? Same metal thickness in all the same spots. Since the 4140 dimensions all yield at the same location and same pressures, how is it different???

Is it the threading of the inner barrel to the exterior sleeve that is the concern?? The cartridge causing the threads to shear internally btw the old barrel and the exterior bushing??

I have in my hand an 1892 Win rifle barrel made sometime in the 50's. Its 45 LC. Its mint on the inside, needs reuse as a rolling block barrel. The barrel is paper thin even at the breech (relative to the rolling block dimensions), has a similar case head diameter for similar bolt thrust, runs similar pressures and has a tenon that is half the length of the roller, half the diameter of the roller (well about 70% is truth) and is using some very fine threads.

How did it survive being installed with half then tenon, fine threads, half the wall thickness in every area, etc??

This is why I am struggling with the concerns regarding the exterior 4140 sleeve.

My DW Model 15 has .75 inch of threads on the receiver end at about 7/16 diameter or less. It endures severe abuse and is prestressed. Its not heat treated, its just a barrel.

Im not being argumentative, please dont take my questions as such. I am looking for facts regarding why failure could or would occur so that my line of thinking can be adjusted. If I keep finding a multitude of examples contradicting the wisdom above, I will continue to scratch my head.

You have responded with what NOT to do or WHAT TO DO, but NOT why? I really am hoping for clarification as to why the responses above were given. Smarten me up dad gum it!! Dont leave me stupid. Teach me to fish, dont feed me.

Thanks to all responders, I appreciate you taking the time. The responses above have stopped me in my tracks.... and Im now looking for alternatives. But I really need the WHY!!

Mike

 

[akajun]

For the gun you don't want to modify, if you would like a fun project, make chamber cast of the chamber, then machine an insert in the shape of the cartridge and chamber it to whatever smaller round you wish to use.

 

[corerftech]

I broke down and bought 8x58RD dies. Ill be case forming next week. I found a parent case Im not willing to specify that is the absolute perfect replacement for the 8x58RD, maybe moreso than an original cartridge!
SSShhhhhh!

Id still love to hear what the failure points are to the first post options for manipulating the barrel!!

I have 3 rifles arriving tomorrow in poorer condition than my first that are candidates for barrel alterations.
Is the 4140 threading going to strip under the 5k or less bolt thrust for the external bushing idea?
Is the barrel going to burst (with external bushing) under 25kspi when it will have a yield strength of 60kpsi +??

Am I compromising the old barrel by reinforcing it with the 4140 bushing of material strength significantly HIGHER than the old crappy barrel steel from circa 189x??
Should I be using prehardened 4140 for greater STRENGTH MARGIN and WHY??

If manufacturers are lining carbon fiber with thin chromo barrel liners and enduring 55kpsi at high cyclical rate, Im not sure how the 4140 bushing CAN fail??
Trust me Im stupid and I really need help here. Not being argumentative. Several folks gave me input that dead ended. "I wouldn't do it" without an explanation.

Teach me to fish, dont hand me a cooked catfish!

Id really like to hear where the failures are anticipated.

With all do respect to the responders!!

Thanks in advance

Mike