PDA

View Full Version : Rebarreling a rimfire to .17?



Doc Nickel
10-14-2005, 06:19 PM
I'm looking at an older Smith & Wesson 422 semiauto pistol in .22LR, and we're toying with the idea of converting it to the new .17 Mach2.

The barrel is an odd design, and would be difficult to reproduce from a blank, but may lend itself to resleeving much like the recent HSM article. Has anyone tried a sleeve, and if so, have you tried one in .17?

Also, I'm aware the impulse is a bit heavier with the .17- conversions for the Ruger 10-22 add weight to the bolt in the form of a tungsten cocking knob. Can I do something similar with this 422, adding something like, say, a stainless T-cocking knob, like the compensated "race gun" pistol shooters use with scoped guns? (This one will have a 'scope too.)

Anything I should be on the lookout for?

Doc.

Paul F
10-14-2005, 06:29 PM
I have no doubt one could sleeve/line the barrel in the 422.

Here are questions to resolve before starting;
Feeding:
Will your existing magazines feed the .17 round?
Or are they easily modified to do so?

Bolt thrust:
Will the weight of the 422 slide retard opening long enough for pressures to drop to a safe level? Or will you start blowing cases as they are extracted when the pressure is still too high?
Will increased slide velocity batter the frame or whatever support member stops the slide?

Physical room:
Is there enough "meat" around the 422's .22 barrel to ream the ID to take a .17 liner and leave enough wall thickness in the original .22 barrel wall for safety?

Safety:
Is there anything, any part or assembly, that will be put under stresses greater than it was designed to take by making the conversion? If that part or assembly fails, will it be "just broken", or will it cause an immediate risk to life and limb?

Not saying you CAN'T do it and make it work great.
But those are the questions you have to answer to your own satisfaction before starting.
I'm not familliar enought with the 422 to help much.
Also, since ammo companies are gun manufacturers are pretty tight lipped when it comes to questons about specific pressures generated by rimfire cartridges, getting the genuine straight skinny on the internal ballistics of the .17 Mach2 is hard. They'll tell you all about the EXTERNAL ballistics, of course.

Hope this helps though!
Paul F.
(was a practicing gunsmith for 15 years).

Doc Nickel
10-15-2005, 06:11 AM
Okay, let's see...


<font face="Verdana, Arial" size="2">Will your existing magazines feed the .17 round?</font>

-I don't know. I was under the impression that the .17 fed from most normal .22LR magazines, being of the same OAL and rim specs.

Supposedly, converting a 10-22 requires nothing more than an appropriate barrel, the heavy cocking knob, and a spring. The factory Ruger magazines are supposed to work just fine.

Doesn't mean mine will, of course, but it's a data point.


<font face="Verdana, Arial" size="2">Or will you start blowing cases as they are extracted when the pressure is still too high?</font>

-No idea. For whatever reason, Ruger announced, then later dropped their .17 version of their .22LR autoloader. I don't know why. Was it too energetic a round for the current build? Financial reasons? Public demand? Feeding issues?

One assumes, however, that one can add enough weight one way or the other. A fair-sized stainless steel block attached in place of the rear sight, a larger recoil spring guide rod (which reciprocates with the slide on this model) and a stiffer spring (assuming one can be found.)

How much more weight, I don't know. That's why I'm asking. http://bbs.homeshopmachinist.net//biggrin.gif


<font face="Verdana, Arial" size="2">Is there enough "meat" around the 422's .22 barrel to ream the ID to take a .17 liner and leave enough wall thickness in the original .22 barrel wall for safety?</font>

-Good question. The stock barrel appears to have been milled from bar stock- flat, not round- that probably started out 1/2" thick. The liner, according to Brownells, is 5/16". So roughly 3/32" walls, plus the remainder of the chambered liner.


<font face="Verdana, Arial" size="2">Is there anything, any part or assembly, that will be put under stresses greater than it was designed to take by making the conversion? If that part or assembly fails, will it be "just broken", or will it cause an immediate risk to life and limb?</font>

-The slide is "captured" by a guide block that's milled into/out of the barrel itself. If that somehow cracked off (it's as thick as the barrel itself, and a smaller bore for the spring) then yes. Other than that, I can see a few places where battering might take their toll, but nothing stands out as fatal if it failed.

(Famous last words. http://bbs.homeshopmachinist.net//biggrin.gif )

The point of all this is that the owner has two of these pistols, and they were never terribly accurate even when new. They were just inexpensive plinkers.

If the barrel were more conventionally shaped, I wouldn't mind picking up a blank and giving it a try. But the shape and design are odd, as I said, probably machined from blanks cut from plate, rather then the usual round stock.

Doing the insert is relatively inexpensive, and in all actuality, probably easier than making one from scratch, but also irreversible if for some reason it doesn't work or won't feed.

Though I suppose I could unsolder the .17 insert and reinstall .22 liner... in which case a careful rechambering may also improve the accuracy ...

Just trying to get opinions here.

Doc.

Yankee1
10-15-2005, 06:10 PM
Hello Doc,
Midway has drop in buffers for 8.99 and the standard spring is six pounds for the 422 it cost 7.49 from Midway. Because all Ruger did was weight the bolt and beef up the recoil spring I'm thinking it sounds like it will work. I think I'd make a dummy cartridge that could be stuck in the liner that would set the ideal headspace when the liner was installed against the bolt.If I remember correctly its about .043".
Wolff has springs, I would find out how much difference between the Ruger std.spring and the spring used in the .17 and get one from Wolff that much stronger.
Sounds like an interesting project.
Good Luck with it.
Chuck

Yankee1
10-15-2005, 06:21 PM
Hello Again,
Doc check this URL http://www.handgunrepairshop.com/17_Mach_2.htm
It appears that recoil spring will be exceedinly important.because of pressure peaks.
Chuck

John Lawson
10-16-2005, 04:54 PM
Lotsa work involved. Tell ya what I did:
Took out my old Crosman CO2 pistol, installed new O rings, left out the CO2 cylinder and simply filled the tube below the barrel to max. capacity with dry ice.
Now it is NOT a firearm and can be fired in the city at varmints. You will be astounded at the velocity it delivers for the first few shots. (If you are any good with a pistol you only need one shot anyway.)
No harm to the Crosman, provided you coat the steel parts with silicone auto wax. After each shot, the tube frosts up like a refrigerator coil.
That's my solution (the simple one) to the .177 craze.

Yankee1
10-16-2005, 08:42 PM
Hello John,
Some people are converting Co2 guns to compressed air using about 2200 lbs pressure. The performance is very good.
I have a few older crosman guns that I'm going to increases the reservoir length on and open up the air delivery passage to the chamber on. In .22 caliber with Co2 they should get a little over 600 fps. With compressed air they will probably go up to 750 fps or better.
Chuck