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Old October 4, 2017, 09:09 AM   #1
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GP 100 Tech questions

Hello all, please don't ask me to sell the gun. I am a tinkerer by nature, and love projects.
This is more a gunsmiths concern, but I find the revolver fans to be very technical. Someone here has the answer.

On a Ruger GP 100 ( 22lr) would the barrel threads in the receiver be the same for all barrels? Specifically, would the 4" full underlug 357 barrel be the same thread? Don't be alarmed. I am not trying to make it a 357 or 38.

If I were to re-sleeve the 357 barrel to 22lr, would I be able to shape the forcing cone in the new barrel sleeve? Or would the cone blend into the factory barrel material?

I realize this may sound radical, but it really is not. I have performed other conversions successfully that I was told could not be done. I love a challenge!!!

The barrel thread is probably the most critical item to the success of this. Everything else I have a work around already.

Thank you for your thoughts and insights. Please contain the flames!!

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Old October 4, 2017, 11:17 AM   #2
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Threads should be the same, but the bore axis is usually higher for rimfire models, versus their centerfire counterparts. (Pushing the cartridges toward the outside of the cylinder for more capacity.)
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Old October 4, 2017, 11:42 AM   #3
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Since you are talking about sleeving the barrel you will need to ream the barrel to fit the sleeve. That should remove the forcing cone and a new cone will be reamed in the sleeve.
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Old October 4, 2017, 11:49 AM   #4
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Pardon my ignorance, but how does the size or shape of the barrel threads have any effect on a sleeved barrel?

I'd think the firing pin would also be in different spots on the rimfire vs center fire.
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Old October 4, 2017, 11:57 AM   #5
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He is going to replace the barrel with a larger caliber gun barrel and sleeve it to fit his 22.
Since the new barrel may not be using the same thread diameter he was asking if it was the same.
The firing pin is already in the correct position in relation to the center of bore.
As long as the threads are the same pitch and diameter he will end up with a heavier barrel on his 22 with a sleeve that keeps it a 22..
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Old October 4, 2017, 08:41 PM   #6
James K
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To answer the question, yes, the threads in the receiver should be the same regardless of the barrel length. Generally, they will be the same regardless of barrel caliber, assuming the frame is the same. (But a larger caliber often means a larger frame and a larger barrel tenon so of course the frame hole diameter and threads will differ.)

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Old October 5, 2017, 08:56 PM   #7
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Thank you all. ShootistPRS you have it exactly right. Yes indeed. I want to install a 357 barrel in 4", with the full under lug. I do understand I would first need to bore it, to sleeve it.

My biggest concern is the threads in the barrel. I don't want to modify the frame. Not even just to bore and tap the thread area. I try to keep any mods I do reversible in case I am not happy with the outcome.

Thank you again
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Old October 6, 2017, 11:56 AM   #8
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Why not buy a GP-100 in 357. I'll grab the popcorn for this one
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Old October 6, 2017, 01:33 PM   #9
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Even if the barrel threads are the same, I doubt many of the other parts you
assume are interchangeable are. Rimfire hammer, VS center-fire hammer,
main spring sizes and strengths, etc. Not to mention the cylinder sizing and
centering issue. This is a situation where even if you succeed, the cost will
exceed the value. If you fail, it may not be reversible.
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Old October 6, 2017, 06:07 PM   #10
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Even if the barrel threads are the same, I doubt many of the other parts you
assume are interchangeable are.
Sounds like he wants a 4" full lug 22, my guess is the rimfire parts will already be on the rimfire frame.
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Old October 7, 2017, 06:57 AM   #11
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Grab some popcorn. I am not converting a rimfire to center fire. I do not want to make my 22lr into a .357 or .38. I am seeking to make my 22lr 5.5" barrel into a 22lr with 4" barrel with full underlug. The 357 barrel is the perfect donor, except for the bore.
The firing pin is already in the right place, in respect to the bore center. I am not changing the cylinder. If the 357 barrel would thread into the receiver, I would first need to bore it, sleeve it, install and index it, cut forcing cone, then set the space between cylinder and barrel extension.

As I said, the thread is the key. I usually can figure out a manufacturers motivations, and could make a good educated guess as to how they would build something. Cost wise, having all barrel threads be the same makes sense. Less tooling, less for line working machinists to think about.
For safety or critical dimensions, it may be another story.

Perhaps Ruger would would tell me the thread size and pitch of the 22lr barrel, if I ask in a way that doesn't make them nervous.

I would prefer to not remove the factory barrel (just to measure threads) if the threads are indeed different. I would simply abandon the project.

And yes, I am fully aware that I should have just bought the SW 617 with 4" barrel in the first place ! :-/

Cost ( within reason) does not factor in. As I said, I am a tinkerer by nature. I find these projects fun and rewarding. Especially when I am told it can't be done. I would expect the cost to do this to be near 300 dollars, and that is fine with me. I do not factor in the cost of tools, as I always buy tools. They become useful for other projects. I have filled 2 complete Snap On stacks over the years doing this.

Thank you again for any insight you may have to offer.

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