Rebarreling a J22 to 17hm2?

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Rebarreling a J22 to 17hm2?

Postby Flowmaster » Sat Jun 21, 2014 3:29 am

I just got the bright idea of rechambering one of my J-22s to 17 Hornady Mach 2 (also called 17hm2). For those unfamiliar, 17hm2 is a 22LR shell casing necked down to 17 caliber. The overall length of the loaded rounds are the same for 22LR and 17hm2 meaning in theory they should fit in the same magazine and hopefully feed about the same way. The reason this crazy idea came to me was because I was thinking about 32naa and 25naa guns. The 32naa is a 380 necked down to 32 and a 25naa is a 32acp necked down to 25. The next logical progression in smaller sizes would be something in 22 that's necked down. That's what got me thinking about 17hm2, a 22LR necked down to 17.

People have been doing 17hm2 conversions on Ruger 10/22s for like ten years now, but I've seen little use of the caliber outside of the custom 10/22 crowd.

I have a friend-of-a-friend gunsmith that did the extended/threaded barrel on one of my J22s utilizing a Marlin micro-groove barrel and a Bentz 22LR chambering. I know that gunsmith is always up for wild projects, so I'm thinking a 17hm2 build on a J22 would be good for the next project.

The icing on the cake is that one of the gun show people I help out on the weekends told me last week he's thinking about getting into engraving for NFA items. That means he'd be able to scratch out where it says 22LR on the slide of my J22 and write something else. I might have him engrave some of my J-guns just because.

My questions for you guys: How safe or unsafe would this really be? I'm not too well-versed in the chamber pressures of 17hm2 or the way it may behave in a simple blowback application. I enjoy having all of my fingers and I'd like to keep them. The last thing I need is a kaboom with Zamak.

Any sources for barrels? I wouldn't need much, just a few inches of 17 caliber barrel. I found a "raw" barrel blank for sale online for $40 and I found the chamber reamer for $75. Beyond that, I don't think I'd need anything else for the gunsmith to work his magic. Doing the J22 threaded barrel project was pretty straightforward for him, so this project doesn't seem like it'd be all that different. It'd be very similar, just with a smaller hole in the barrel and a different chamber cutter. I'd be in it for like $125 including shipping just for the reamer and barrel plus whatever for his time.

Thoughts? How crazy is this idea? Am I going to lose a finger or two?
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Re: Rebarreling a J22 to 17hm2?

Postby FergusonTO35 » Sat Jun 21, 2014 11:31 am

As long as the pressures are similar I see no reason why it wouldn't be ok.
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Re: Rebarreling a J22 to 17hm2?

Postby Flowmaster » Sat Jun 21, 2014 9:14 pm

As far as strength, I'm not really afraid of kabooming due to pressure. The thing that I've been thinking about is the spring tension of holding the action closed for the right amount of time or being strong enough to not batter the frame.

Anyone ever shot anything chambered in 17hm2?
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Re: Rebarreling a J22 to 17hm2?

Postby FarmallB » Sun Jan 29, 2017 9:37 pm

Flow, did you ever pursue this project any further? Sounds like fun. It seems like a pretty straight forward swap. I would'nt think pressures would be that much different.
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Re: Rebarreling a J22 to 17hm2?

Postby Flowmaster » Tue Jan 31, 2017 12:37 pm

No I didn't, mainly because I couldn't find anyone to do it. I don't have the capabilities to do any chambering myself. Someone else here totally should though.
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Re: Rebarreling a J22 to 17hm2?

Postby farmkid » Wed Feb 01, 2017 3:04 am

Dang, that sounds neat. However, some quick googling shows that it's not straightforward. From a Shooting Times article from 1/4/2011:

"...time-to-peak chamber pressure for the .17 HM2 differs from the .22 Long Rifle.

In addition to causing bolt-cycle speed of an autoloader designed for the .22 LR to increase beyond an acceptable level, it could also cause the bolt to open prematurely, allowing a fired case to start moving from the chamber before pressure had dropped off. In other words, converting a semiautomatic in .22 LR to .17 HM2 required more than barrel replacement. The problem has been solved by either increasing the weight of the bolt directly or by indirectly adding weight to the bolt by linking it to a reciprocating weight hanging from the barrel and located inside the forearm, as Thompson/Center has done with the R55 rifle."

But it's a great dream if someone can figure out how to do it.
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Re: Rebarreling a J22 to 17hm2?

Postby Flowmaster » Fri Feb 03, 2017 12:18 am

The only way I can think of adding mass to the slide would be to stick some lead wheel weights onto the exterior of the slide. Those stick-on style wheel weights are great and the adhesive lasts forever.

I'd be really afraid of some out-of-battery discharges. That could get nasty really fast. I've seen more than a few blown out 22LR shell casings in my journeys and I wouldn't want to see it with another caliber.

Doing more weight on the slide in conjunction with a brand new recoil spring would probably help keep it safe. In the event that it did want to blow out about a third of the shell casings, I wonder what kind of damage that'd do to the gun? Zamak is soft so would it crack or bend or something?

Now I really want to do this even more. I'm going to have to talk to a couple of guys when I'm at the next gun show. A friend-of-a-friend type of deal might get the ball rolling on a project like this.
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