Hello All,

I'd like to consider 9mm as an ammo option for my 642 J-Frame. I have seen references to 442s having this option but not my model.

1- is it possible;

2- if yes must a 442 cylinder be installed, or the 642 cylinder be machined, or is there a 642 cylinder available already cut for clips.

Thank you.

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-gonzo, SoCenPA.

I don't think that would work very well, for a couple reasons:
A.) 9mm uses bullets that are 0.002" smaller, which will make accuracy suffer when fired from a 0.357" barrel. (And velocity will also suffer due to a poor seal.)
B.) 9mm is a high pressure cartridge, running at 35,000psi--the same pressure as .357 Magnum. (.38 +P, by comparison, runs at 20,000psi.)

To make it work, it has to start with a .357 magnum revolver, and it should really get a new barrel. You could check into a S&W 940; a 9mm "640" (stainless j frame .357 magnum.)

Can it be cut for moonclips? Yes. See moonclips.com
Does that mean you can then automatically use 9mm? No. The moonclips.com modification and clips are for use with .38.

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Science plus Art

Question. Why do you want to put 9mm in your 642? Does 38sp+P not provide enough defensive power for you?

My 642 is the Pro version which has the cutout for moon clips from the factory and gives me an option to use them or not use them. Still, it's 38sp only. Love that gun.

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Still carrying my S&W 642

The answer is yes. I had TK Custom cut the cylinder of my 642 for 9mm moonclips and it worked just fine. I've since sold the gun to another forum member (whose name I can't remember); maybe he'll comment on the gun.
I didn't have a bit of trouble, even with +P loads. Some of the 940s had trouble extracting cases due to rough chambers; the chambers in my 642 were polished glass smooth by Tom when he did the work and there was never a problem with extraction.
Recoil with +P loads was very noticeable, but about the same as .38 Special +P loads in the same gun. Accuracy was equal between the two rounds.

Your existing 642 Cylinder can easily be machined to allow the use of moon clips with the current 38 Special chambering. Once this is doen you will have the choice of using moon clips or not.

Your existing 642 cylinder can also be easily rechambered for 9MM ammunition (in moon clips only). Once rechambered, the firearm will no longer be a 38 Special.

Converting a 642 to 9MM is not a wise move. The alloy frame is not designed for those stresses

Converting any of the modern stainless 640s is just fine. Also any of the Scandium framed Centennials like the 340s or 342s would also be a safe conversion.

As to accuracy, the Urban Myth that firing a .355 projectile through a .357 bore will not be accurate was started by people that do not understand the relationship of bore diameter, grove diameter and projectile diameter.

As long as your projectile diameter is larger than "Groove Diameter" you will be engaging the rifling and imparting spin on the projectile. An extra .002" of engagement does not change how much spin is imparted or increase accuracy.

I have been running .355 projectiles in .357 S&W bores for more then 3 decades now.

Here is a current 357 Magnum model 627. It now has a second cylinder that is chambered for 9x23 Winchester. The nice thing about moonclips is that the 9x23 cylinder can chamber and fire 9x23, 9x21.5, 9x21, 9x19, 9x17(380ACP), 356TSW and a host of other cartridges.




This Smith & Wesson 940 has been rechambered for 38 Super. Like it's big brother above it allows for a large list of 9MM based cartridges to be fired.




If you are a handloader, firing cartridges that the revolver is not specifically chambered for will result in brass that is hard to resize or not suitable for handloading.

I apparently was confused about using moonclips. I'll leave well enough alone.

Thanks to all for weighing in and providing all this information.

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-gonzo, SoCenPA.

Thread resurrection...., I know -- but this item (of mine) is likely of interest to those who still are following this old thread.

http://smith-wessonforum.com/accesso...#post138946509

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-Chris