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How to turn offcenter barrel?

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oughtsix

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#1
Any one ever turn a barrel so the bore is eccentric? I've seen it done by an old dead guy to use a center fire breech for a rim fire cartridge. A youtube would be great, but all I find are for cutting a hole in flat stock, or turning a crankshaft. If any one has experience, I have questions...

thanks

-06
 

Tony Wells

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#2
That's a pretty good trick for an old dead guy. Too bad it wasn't taped.

You have to make a exact match pair of eccentric bushings that clamp on the barrel, and make sure they are "timed" perfectly. They need to be heavy enough walled to not distort when chucking and run in a steady rest or outboard spider if you have to swallow the barrel. I've not done a gunbarrel, but the oilfield is full of precision offcenter features, and some at precise angles with the apex at a very specific point "out in space". So while not doing gun work, I have done a great deal of the same type of work on other parts. Many, many.
 

Silverbullet

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#3
Don't you only need the breach end off center to use the firing pin on the edge of a 22 shell. For that you could just make a chamber adapter. Just asking , if you offset the bore the bullet path will follow the same line.
 

Tony Wells

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#4
I believe he is referring only to making up the threads on the barrel to offset the entire bore and chamber to align "offset" to the action so that the existing firing pin on a centerfire action strikes the rim.
 

Silverbullet

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#5
I believe he is referring only to making up the threads on the barrel to offset the entire bore and chamber to align "offset" to the action so that the existing firing pin on a centerfire action strikes the rim.

If that's the case he needs to figure out the difference between them . Setting the barrel up in the four jaw with his indicator for the difference , then his spider can be set up the same to turn the barrel offset. So I guess he's cutting the chamber off and starting over? Should work but the forearm may fit different . What kind of gun ?
 

Tony Wells

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#6
Cutting the chamber off and shifting it out of line with the barrel bore isn't the answer, obviously, but if he shifts over ~.110 with the threads and then deals with the now eccentric barrel OD and how it fits in the stock, you could use a 4 jaw and spider, but I'd think getting the "high point" of the eccentric exactly in line on the inboard and outboard ends of the barrel would be the trick.

Of course, clocking the eccentric so that the offset is correct to align with the firing pin might be a little tricky too. Lots of unexpected things happen when you start machining angular parts or eccentric parts on the lathe. Have to do a lot of 3d thinking.
 

oughtsix

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#7
I have a drilled tube that will eventually be a barrel for a double set trigger Ballard. I did wonder if I could off set the breech end and have the bullet exit a "centered" hole in the muzzle. Am not sure if that would work, if it would that would be the easiest route, maybe.

I had not thought about threading yet. Guess I thought once the barrel was turned eccentric to the bore, the threading would be as normal concentric to the outside. I would expect a bit of trial and error getting the bore indexed to the firing pin.

Have to do a lot of 3d thinking.
Not very good at that, as a rule.
 

Tony Wells

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#8
Your exit path for the bullet would be at an angle to the barrel OD. Sighting it in would be just about impossible.
 

sgisler

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#9
I would think the less complicated way to do it would be to modify the breech block. i.e.: link it higher or lower or remake one with the firing pin aligned for rim fire.


Stan
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rgray

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#10
Have you seen this video?
Interesting centerfire rimfire switch over on some ballards.
 

oughtsix

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#11
Some Ballards have a reversible firing pin. The one I have and the one I considered buying were center fire only.
 

sgisler

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#12
Is the breech block of the typical 2 piece construction? If so, I think making the modification there has got to be your best bet.


Stan
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Reeltor

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#13
I don't know if it is right or wrong but I've watched several manufacturers chuck the barrel blank between centers and machine the exterior of the barrel. They chucked a hunk of aluminum in a 3-jaw chuck, turn a 60° angle on the aluminum. Now that center is concentric with the center of the lathe. Chuck the barrel between these and then cut the exterior of the barrel.
 

oughtsix

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#14
Yes , two piece breech block. My idea was to have one rifle I could shoot with one barrel and then switch to a center fire barrel .
 

sgisler

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#15
Ah, ok. Switching back and forth does make it a little trickier.
You could emulate the Ballard reversible firing pin, hard part would be to make the switching external. Seems that the T/C Contender had a switchable firing pin in the breech face. Might be worth a look for ideas.

I have a contender, I will take a look at it this evening. Can't remember if it's centerfire only.

Stan
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Silverbullet

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#16
Could you drill the receiver and add a second firing pin ? With a pin thru the side to hold it in . Not a hard job I don't think . It would mean removing the other pin or make a new block with the pin offset .
 

bob308

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#17
pope made a high wall that had an eccentric for a hinge pin. turn it one way and it lowered the breach block to fire rim fire. turn it the other and it would fire center fire. .
 
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