9mm conversion cylinder work

[jeep45238]

Warning- ideas provoked by a week of 3-4 hours of sleep a night.

I’ve been daydreaming about having TK Custom machine the cylinder of my k frame to accept moon clips and 9mm.

They claim that after machining the revolver will shoot .38 and 9mm, with the caveat of staying with standard pressure 9mm to avoid sticking brass.

How would this impact shooting .38? Sticking any more of a possibility than without the caliber conversion? How would the higher pressure/lower weight of the 9mm treat a .38spl only k frame long term (durability issues)?

Having two calibers in one gun sounds mighty nice - and if proven means stocking one caliber. Best part is it’s less than a 1050 caliber conversion w/ toolhead to reload 38 spl.


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[Screwball]

I tried .38s once through my Pinnacle converted cylinder... they stuck (wanted to see if I had to run it that way in an emergency). Never had an issue with .38s in a .38 cylinder. Never had an issue with 9mm in the converted cylinder. Only issue I ever had was shooting .38s, then .357s in a 686.

I only shoot standard pressure, usually 147 grain, out of my J-frame... more because it is an Airweight. For a steel K-frame, I wouldn’t shoot +P religiously, but probably would try a cylinder of them to see if sticking occurs. If I had a 640, even if one of the .38 ones, I’d likely be less worried about pressure. Probably would train with standard pressure, using +P for a percentage of training, and carry that. For durability, Airweights have been converted on S&W Forum for years. S&W also did a 942, which didn’t go past the prototype (Wiley Clapp tried it, and said it would never sell). If I had any question of it being an issue in my gun, wouldn’t have done the conversion.

Also, if you really want to shoot .38s, buy an extra cylinder, have it fitted to the gun, then have that converted. Gives you a conversion with pulling one screw. That is what I did with my 642-1, mainly because it was already redone in NP3 Plus. Once the cylinder was fitted (bought from a member on AR15.com), sent it to Robar to match.

[JodyH]

My experience with a Ruger LCR 9mm is that the concept of 9mm through a revolver is great.
The reality was that bullet pull was a major issue with every ammo I tried, some worse than others but they all pulled.
Even after finding one that pulled less than the others the amount of pull still varied enough to concern me.
I had the best luck with Magtech 93 grain solid copper hollow points (super light bullet resists pulling forces better), but their terminal performance is severely lacking.
The heavier the bullet the more they pulled.
None of my favorite carry loads worked to my satisfaction which pretty much killed my whole reason for wanting a 9mm revolver.

[jeep45238]

Well, that puts a damper on it for sure. Do you think the problem would be mitigated by a heavier revolver?


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[JodyH]

Well, that puts a damper on it for sure. Do you think the problem would be mitigated by a heavier revolver?

Yes.
The heavier the gun the better.
The lighter the bullet and the tighter the crimp the better.
You want the gun to move as little as possible and you want the bullet to move as much as possible with the gun.
A heavy bullet tends to want to stay in place (Newtons law of inertia at work) while the case goes rearward since it's locked to the cylinder.
If the case-revolver combination going rearward overcomes the crimp due to the bullet wanting to stay in one place you get bullet pull.
A lot of the FMJ practice ammo will pull enough by round 4 out of 5 to completely dislodge the 5th bullet and leave it and the powder just floating around in the cylinder.

[JodyH]

The easiest way to quickly check for bullet pull at the range is to get a wide tip Sharpie marker and stripe all your ammo bullet to case.
Shoot 2 or 3 then look at the remaining rounds.
If they are pulling you'll see bright shiny bullet copper at the crimp as the un-Sharpied portion of the bullet starts coming out of the case.

[willie]

You might find out what dimensions change when the cylinder conversion is done. About bullet jumping. The reloader can circumvent this issue. I can discuss how but wish not to drift from your question.

[jeep45238]

You might find out what dimensions change when the cylinder conversion is done. About bullet jumping. The reloader can circumvent this issue. I can discuss how but wish not to drift from your question.

I’d like to hear it, assuming it’s relevant to 9mm. I don’t mind doing some adjustments on my dies to make it work.

[Screwball]

For crimp jump, more emphasis should be put on the crimp over weight. Manufacturers can be better/worse, but it really comes down to crimp. If it is a crappy crimp, doesn’t matter if it is 115 or 147 grain... likely will have movement.

From what was said, heavy bullets and light guns, my combination shouldn’t work at all. Hornady crimps are probably one of the best. I shot UMC bulk 115 grain for practice, and no issues either. As mentioned, if you want to check for crimp jump, load up a moonclip and fire all but one round. Realistically, that is the most any of your ammo will have to face, since it will be shot last... if it holds tight for those, you should be good. Some people try multiple clips with the same round to test out the crimp.

[BN]

.38 Special is a straight wall cartridge with a diameter of .379" for the whole length of the case.

9mm is a tapered cartridge with a diameter of .380" at the case mouth and a diameter of .391" at the rear of the case.

To rechamber a .38 Special to 9mm, the rear of the chamber must be opened to allow the larger 9mm to fit.

Probably .38 Special could still be fired, but the 38 brass will swell to fill the space of the 9mm.