Minimum breech diameter

[Donaldo]

Ok you engineers I need you to dust off your slide rules.  (dates me huh).  Lets assume a handi rifle, in say 243 Win.  What would you estimate the minimum diameter of the breech could be and still be safe.  I know the muzzels get pretty small on some but then the pressure is down by the time the bullet gets there.  On the breech I guess the max pressure should be about 65,000 psi.  What would be standard safety factor 2 to 1.  Got an idea that keeps knawing at my brain and don't have the necessary gray stuff to figure it out.

[Leftoverdj]

Skip the math. Somebody else already did it. Breech can be as small as the  smallest shanks of barrels threaded the .30-06 family of cartridges. That's around .90. If I run across my list of threading sizes, I'll post again.

[Fred M]

Donaldo

Approx. Barrel steel Ultimate tension 65-70 Ksi (Kips sq/in)
Elastic limit 34 KSI
modulus of elasticity 29,000000 lbs/sq inch
Elongation % =Tensile strength  1,50000/Tensile strength.

If you going to turn down a barrel on the chamber end these are approx guide lines. Do you know how strong this steel is? Most chamber ends are 1.200". the Handi is 1.100". Besides how much weight do you think you can loose by slimming the chamber end. Steel weighs 0.283 lbs/cub inch.

If you have a MS Excel program I can send you a Excel program that calculates barrel weights for both round and octagon.

[Donaldo]

Fred,
You give me a bunch of numbers that I don't have a clue as to what to do with them..  Ok... here is my idea.  And it was not to reduce the weight.  My thought was to take a shot out barrel or a good one, don't matter which.  Cut the breech and lug off, leaving a stub of about 3-4 inches, just enough to hold the scope rail.  Bore this stub out and thread it internally.  Then take a barrel of any make, say Remington take off.  You can get new take off's on ebay for $50 or less.  Turn the breech down to a diameter and thread it so that it would screw into the short stub.  You might even be able to get a barrel nut on it like the Savage bolt guns.  Or just leave a shoulder on it.  That would get you around having to find a lug and weld it onto a new barrel.  That way you could have the one "short barrel stub with threads" (kind of like a receiver) that fit your particular frame and just change out the barrels.  On the Savage bolt rifles, a barrel change out is about a 15-20 minute job, and you don't need a gunsmith to do it.  Just unscrew the nut and barrel, screw on the new barrel, head space it on a gage or fired case from that chamber or a new case, snug the barrel nut down tight and you are finished.  Presto.... a new rifle.  I am just not sure we have enough material there to work with, that is why I was asking the questions about minimum diameter, etc.  Come on Fred, put your thinkin' cap on.  This would work, I think, and that usually is a problem when I start to think.  

[Donaldo]

I forgot to put this in my last post on this thread.  It might be that the only cartridge or cartridges you could do this on is the .223 family or on the lower pressure pistol rounds, like the 357, etc.  Might not be enough material left for the 243, '06 family case diameter.

dj.... I think the old Kimber barrel was threaded at about 0.820 if I remember right.  There may be others smaller, I don't know.

[Fred M]

This is a different story. The threaded part is where the trouble is. In order for threads to be removable they have to have clearances.

We have on the Handi a 3.500" parallel section which is 1.110 O.D. the one I have. For safety reasons we have to assume that this is the O.D you need to safely restrain the chamber pressure..

The radial chamber wall is 0.320" on an 06 type case. If you were to take 1/2 of that and leave 0.160" by drilling a 0.790 hole, you have in effect cut the design strength in halve.

The same goes for the tenon to fit the hole, since a threaded tenon can't be considered a unified body because of the clearance in the thread you are working on the edge of safety.
A very fine unified thread may work. I don't know much about threads but my machinist friend will tell me.

What you have to get is, the two pieces have to be totally unified in order to retain safety standards. Both have to share the load.

A Rem 700 standard 22" barrel is 0.950 at 3.5" from the back, that would give you a 0.080 shoulder. Of course this barrel would have to be installed with torque and a barrel vise. I let you know what kind of thread would be best. It goes without saying that the treads will be have to be perfect.

Of course with a smaller diameter case you would be better off. But I still would use the 50/50 ratio tenon/sleeve wall.

If you could make a very shallow Acme thread and heat shrink the tenon in place you would have a unified body again which would be a permanent installation.

But if you want to heat shrink the tenon then you wont need no thread, just glue the two together with epoxy. My self I would go for a non interchangeable barrel. 100F above room temp will give you close to one thou. Temp change of 100F x 0.00134 will give you surface or radial expansion. Longetutional is halve that for medium steel.

Also you should not weld the new forearm barrel stud. This would completly ruin the stress relieve of the barrel. Low temperature solder and small 6-48 screws plus a sadddle on skinny barrels.

[Mac11700]

Fred,
You give me a bunch of numbers that I don't have a clue as to what to do with them..  Ok... here is my idea.  And it was not to reduce the weight.  My thought was to take a shot out barrel or a good one, don't matter which.  Cut the breech and lug off, leaving a stub of about 3-4 inches, just enough to hold the scope rail.  Bore this stub out and thread it internally.  Then take a barrel of any make, say Remington take off.  You can get new take off's on ebay for $50 or less.  Turn the breech down to a diameter and thread it so that it would screw into the short stub.  You might even be able to get a barrel nut on it like the Savage bolt guns.  Or just leave a shoulder on it.  That would get you around having to find a lug and weld it onto a new barrel.  That way you could have the one "short barrel stub with threads" (kind of like a receiver) that fit your particular frame and just change out the barrels.  On the Savage bolt rifles, a barrel change out is about a 15-20 minute job, and you don't need a gunsmith to do it.  Just unscrew the nut and barrel, screw on the new barrel, head space it on a gage or fired case from that chamber or a new case, snug the barrel nut down tight and you are finished.  Presto.... a new rifle.  I am just not sure we have enough material there to work with, that is why I was asking the questions about minimum diameter, etc.  Come on Fred, put your thinkin' cap on.  This would work, I think, and that usually is a problem when I start to think.  

Hmmmm...sounds like a David White special to me... :?

Mac

[cheatermk3]

So, Donaldo, you're talking about a way to make a switch-barrel gun out of an NEF rifle?  like a universal barrel block to which you'd fit whatever barrel you desire?  The reason for this would be what?  To have calibers that NEF does not offer?  I don't think this would be a money-saver over finding the right bore size for the caliber you want and rechambering.  

Not trying to flame here, I just don't see the point, when you're done you still have an NEF rifle, with all of the design limitaions that come with it.

Seems like all hhe fitting that your idea would require would cost more than a new rifle, plus the rechambering cost.  

Can't fault you for tryin' though.

[Mac11700]

If you got everthing you need to do the job and can mate both together perfectly...there really shouldn't be any reason why it couldn't be done like that... David White has been offering this conversion...or " Stubbing" for some time now...don't know how good he is or the quality of work he does...and if I remember right..the cost was around $350-$450 for him to do it....seems like you could get anytype  or lenght barrel and have what you want... of-course staying within the pressure limatations of the receiver would be a priority...and then having the front barrel stud welded on..or screwed on...depending on the barrel thickness...you would definatly need to do it on some precision equipment to get it perfect... but it sound feesable anyway...

Mac

[Donaldo]

I have heard of David White but don't know much about him.  And I haven't read about what services he does.  Does he have a web site?  My main focus here was to get a 6mmBR barrel without having to go thru the process of getting a barrel of the correct dia. and then finding a latch lug to weld to the barrel, yadda, yadda.  I really don't care if this is only a $200 rifle.  I think that it would be an interesting project is all.  I am not trying to re-invent the wheel.  But if any of you have Savage bolt rifles and have switched barrels you know what a simple deal it is.  If you have a Savage bolt gun and haven't switched barrels, then maybe you need to.  Come on Fred, seems only you and me see the possibilities here.  And by the way, I have about 0.030" clearance between my 1.100 breech and the sides of the Handi frame.  That means an additional 0.050" or so could be added to the dia. of the breech/action.  Not much but a bit of help.

[quickdtoo]

Donaldo, should I post the original thread on D White??? You might not like it.... :oops: Does the thread below ring any bells???\

http://www.graybeardoutdoors.com/phpbb2/viewtopic.php?t=50780&highlight=david+white

[Donaldo]

Is that who they were talking about?  I thought it was that guy whose name starts with Bel...  I don't think I have posted anything about David White, other than maybe asking a question.  Seems I remember some talk about him a while back, but nothing specific.  Is he not to be trusted?

[Fred M]

Donaldo.
Like I said I will investigate the unified thread. To add a sleeve to the out side would not do anything be cause it is open on the bottom like a horse shoe.Unless you  do it by installing two rows of high tensil screws along the underlug torqued to the allowable stress of the screws and threads.

The underlug would bridge the gap and make up support there. All this is a big job and it would require some good machinist skills. The number of screws required is equal to the x-sectional area of the sleeve calculated in single shear. I would also use epoxy for this joint.

One thing I will not supply you with calculations of stresses for use of this undertaken. Not that I think it is not safe but I am not qualified to supply them.

How many barrels are you planning to switch. I f you only want a 6BR or a 6PPC  then get a 22 Hornet and have it rebored and chambered. The BR or the PPC  will clean up the Hornet bore and chamber. That is what I would do.

Another very nice one is a conversion of the 223 to a 6mmx47 this is one of the finest 6mm's for a hunter. It is based on the 222Rem Mag case.
My barrel maker has a reamer and that is what I think I will going to do next. I would have a 1-12" twist? This chambering has superlative accuracy. Ok to shoot a deer in the ear at 200 yards.

It would be very suitable for the Handi lock up with the lesser back thrust.

That and the 257 Roberts would be a good one for H&R to make. Remington used to make a factory rifle in 6x47.

[Donaldo]

Thanks Fred,
It was just an idea.  I didn't really think there would be enough material left to do it like I wanted to.  Oh well..... on to the next crazy idea.  Wish the weather would get better so I can go bust some caps.  Need to shoot my handi.... and some of my other guns too.

[Fred M]

Donaldo.
Now after all this you throw in the towel, with the outside sleeve to make up for the thread. This is a workable plan. Hey the sleeve may not be needed if you get stub heat treated or could make a custom stub with high tensile steel and added diameter. I understand the underlugs are available :-D  

[Leftoverdj]

Threading would bother me. You don't have a lot of metal to work with and you are weakening it by the depth of the threads. Stub a barrel, ream it to 7/8", and silver solder in a new barrel if you wanna.

Even then, I'd wanna use an SB-2 barrel for the donor and I'd be mighty careful about how hot I got the lug.

Seems to me that it might be simpler to just have an artist with a TIG weld the lug onto a new barrel if you are talking PPC diameter cartridges. Stub and silver solder would be OK for smaller cartridges.

[Donaldo]

Well yeah you could go the silver solder route and fix it permanently.  If I have to do that I would just get a lug and have it welded  to a new barrel.  I have found a welder than said he could weld the regular steel that the lug is made of to a stainless barrel if I wanted it that way.  That was the main thing my 'smith was concerned about.  The main thing about the "stub" was to get a sort of receiver that you could then screw different barrels into, like a Savage bolt rifle.  I am still going to think about it some but it is on the back burner now.  I have a new Savage 110 in 243 that I am working on, got one of the Walmart close outs for $250.  I bought a new take-off Savage 223 HV barrel and and going to do a switch over.  Will have to get a 223 bolt head for the Savage bolt and a barrel nut wrench, but I can do the switch myself.  The Savage system, while scoffed at by some, is sort of a modular system and very clever engineering.  Change out a barrel, change out a bolt head, presto, a new rifle.  The bolt head sort of floats on the end of the bolt and lines up very well with the bore.  Besides, I have another custom Mauser 243 that I am bored with and need a new project.  Plus of course my beloved Handi in 223 UV.  Anyway, just shooting the same old thing over and over gets boring to me.  Can't keep the ole brain from thinking about these things.    

[Fred M]

Donaldo.
Had to go back to the machine shop to day to do a new crown on the octagon barrel since the milling had damaged the old one.  I had hoped  the barrel maker would do a new crown. But since I had not specifically asked for it it was left undone.

To set up a tapered octagon barrel for a new crown, is not all that easy.
You have to make eight shims to allow for the taper in 4-way chuck. Make a brass rod to fit inside the bore to to center the bore with a dial gage.
5 min. for the crown and two hours for the set up. I can see why the barrel maker forgot to do it.

Had a long discussion with my friend. about threads and stubs for the Handi.
 
The barrel with the thread on it has to be a stand alone on pressure, because there is no kind of thread that will unscrew with out clearance.
So the outside sleeve part can only be considered as a retainer of the barrel and 1/10 radial thickness on top of the thread would leave you with insufficient material for the barrel.

So the only wat to make a barrel stub is to silver solder it in, this would restore the strength integrity. In any event that is not a bad deal to restore a Handi  with a bad barrel and that was the conclusion other poster have mentioned. So I guess a switch barrel is pretty well out with a Handi.
It still can be done according to my friend but it would be a very costly undertaking and not practical.

Yes you are right about the modular Savage system it has lot going for it.
Switching is easy and without a hitch. On the other hand a switch barrel rifle is not the greatest cats meow either. I have a 30BR switch barrel  for my 25 Hunter HBR rifle, but would rather have two seperate rifles.

[Donaldo]

Fred,
Thanks for the input.  I figured that there just would not be enough material on the stub to do what I wanted.  As an after thought, today I was looking at the first center fire rifle I put together many years ago.  About 35-40 as I recall.  It was an old Jap 6.5.  It was in pretty good condition for what it probably went thru.  A friend rechambered it with a home made reamer for what was more or less a 6.5x257AI.  Used the old barrel and actually it shot pretty good.  Anyway was looking at the stock for another project and got to looking at the barreled action.  I had removed the old rear sight to get a cleaner looking barrel.  The barrel looked kind of skinny so I miked it.  It was 0.750 at the breech about 2.1 inches ahead of the receiver.  There was a swell of course where the cartridge went, but it was only 2.1 long.  The case was about that long.  Essentially what all this rambling means is that in this barrel, the bullet was probably about where the barrel went down to 0.750 dia.  I probably shot 200-300 rounds thru it, some pretty hot and no problems.  Not that any of this means anything but that thin barrel held a lot of pressure for a wall of about .250 inch at the breech.  It tapered down to about 5/8 at the muzzle.  Have no idea what kind of steel it was, other than carbon, but have always heard that the old Jap action was about the strongest ever made.  The dia of the receiver is about 1.115, odd that that is about what a Handi is.  Anyway.... have fun with your project..... it don't have to be practical if that is what you want.  

[Fred M]

Donaldo.

it don't have to be practical if that is what you want.

You are right about that, what I meant was you would really have to dig in and find all the right stuff, and fire a proof load.

Here it goes the revised calcs. Take existing H&R barrel stub of 1.110 and drill a hole o..886 and put in a 1/16" thread .062. (.050=0.062 is the wall with thread)

A sleeve with 1/16 thread .o625" +a nd 0.050 wall = .112 x 2=  .224 -  1.110= .886" - . 06 case diameter of 470+.010 +.010= .490. 886- 490= .396 : 2= .198 the ring around the cartride. This is what you have to work with outside of a 308Win. chamber at the back end a bit more at front of the chamber.

Take an existing barrel and turn it to .490 for 3.5" length that will give you 10 thou otside the chamber. Now you find a piece of steel with a 275Kpsi
tensil strength and make a sleeve to fit over .490 barrel end and siver solder them together and turn it to 0.886+ .062 for the thread. That will give you a .198 H.T. ring of steel plus 1/2 the thread for a total of 0.229."

Maybe I am just halucinating. :-D    Edited. You get it?. If you take a pair of dividers and double the size and draw it on a piece of paper you can see it better. Or just draw circles by hand.

[Donaldo]

Fred,
Maybe you are  halucinating.  I am not sure I can follow you figures above.  But I will cogitate on it seriously.  Thanks for all the input guys.  Probably time for this thread to die.  Still think it is a good idea but not practical.

[Fred M]

Donaldo
I will edit the above so you can dig it.