Info on TK Custom 9mm conversion

[john c]

I don’t have a 9mm/.38 conversion, but from my revolver reloading experience, I think the biggest issue in accuracy is bullet to throat fit. A .355 bullet in a .358 throat will yaw and hit the forcing cone in unpredictable ways, causing accuracy deterioration. If your throats are tight, this will be less of an issue. You could easily have a .356 9mm bullet (some are this fat, especially cast lead) in a .357 (on the tighter end) and have it shoot fine.

Another owner could just as easily have .359 or .360 (rare, these days) throat and have a .355 bullet be much less accurate.

The worst situation is when your revolver throats are all over the place, like 4 at .357 and 2 at .360. It will never group until you hone out the throats to a consistent diameter. Throats this out of whack were much more common in ‘70s and ‘80s era guns. More recent decades have seen vast improvements in consistency.

I’m glad you have good luck with yours.


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[JimCunn]

Two years later, the 9mm J-frame conversion is still my favorite carry.

SAAMI spec for land and groove diameter is identical for the 9mm, .38Sp, and .357Mag.
I've not noticed any accuracy degradation.

[JimCunn]

Am currently working on a .380 conversion, but am not happy with it yet.

[JCN]

Am currently working on a .380 conversion, but am not happy with it yet.

Can you elaborate and add more detail? I would LOVE to do this, but I don't know where to begin. What is the donor cylinder?

I tried shooting 380 out of a J frame by just using moons and it was doable but accuracy and velocity was terrible.

Thanks!

[JimCunn]

Donor cylinder is a J-frame titanium .38Sp/.357Mag from Midway. Moonclips for this first trial are from a Taurus .380, but the Taurus cylinder circle radius is a bit too big, so they are slightly offset from the forcing cone. They will chamber in my 9mm cylinders, but I don't think they will in my .38 cylinders. Gotta get em concentric. Family Christmas doings are kind of slowing down my efforts.

I expect to see muzzle velocities on the loose order of 650 fps, combined with lousy accuracy. I like shooting my J-frames at 25 yards, but I doubt the .380 conversion will be up to that.