I posted this in my other thread but I felt it deserved it’s own because I have heard differing opinions on it. The question was whether the .38 special cylinders in the K frame (and the Model 10 specifically) had a different heat treat or wall thickness than the .357 magnum versions, well now we know, per Smith and Wesson themselves via email, so now the question should be settled, here is their response:

The heat treat specs are the same on the model 10. The wall thickness between the 38 and 357 is the same, what is different is the depth of the bullet seat. We do not support changing the caliber from the caliber that it originally left the factory as.

Thank you for choosing Smith & Wesson.
Have a great day!
Regards,
Carolyn

So it seems that there was indeed no difference in either the heat treating or wall thickness, however (predictably) Smith and Wesson still does not recommend converting .38 caliber cylinders to .357 magnum, likely for legal CYA reasons as there is apparently no mechanical reason not to.

Makes sense. I had a 10-6 that was chambered in .357 Magnum, and I would not hesitate to cut a special for magnums if I couldnt find what I wanted.

Good useful information. Maybe now the handloaders that are scared to death about loading anything but squib loads in their .38 spls can add a couple tenths of a grain of powder to their loads without losing sleep.

Thanks much. This is great info for all of us and settles the +P question in 38 Special K frames. I do agree with S&W about any of us not changing a Special to a Magnum since I would not trust anyone other than the factory to do that operation safely.

wait a minute........So........Technically. I could change the cylinder on my 15-3 to a .357 and ping pow away? Hmmm Or......overload past +p in .38 and make a .38 magnum.

Dangerous.........I like dangerous :-p

Not without recutting the barrel extension and forcing cone. 357 Magnum cylinders are longer than the 38 Special cylinder. Yes, you could "magnumize" 38 Special cases, I'd suggest keeping it to 38-44 HD levels and definitely keep them out of other revolvers chambered in 38 Special or older K-frame and J-frame S&W's.

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VCDL, GOA, NRA

I have 2 custom K-327's using K22 cylinders. Haven't had a problem yet.

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Chris
SWCA #2243 SWHF #292

Although I have been preaching this gospel for years (and have been raked over the coals by many here because of it) the question that remains is a crucial one.

Eventhough S&W confirms equal heat treatment specs for 38 and 357 cylinders TODAY, is it the case that cylinders have ALWAYS been hardened identically?

I believe they have been. Perhaps that is why my 60 year-old Model 10 cylinders have survived gazillions of 30,000+ psi rounds.

Actually I am surprised they told you this. Not questioning you, but ssurprised.
I remember the gun rag questioned the heat treating between both and cautioned against it.
Maybe it was over fear every Tom, Dick, and Harry, would set about reaming their Charter Arm chambers and blasting away.

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I told you not to use Lifebuoy

Heat treating both 38 Special and 357 Magnum cylinders the same, to me, makes economical sense.

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VCDL, GOA, NRA

I asked specifically about a 10-6 so presumably it has been true AT LEAST that long so I would consider 10-6 and newer safe for high pressure, but I would not be surprised if older ones were too though. Fun fact, Smith and Wesson actually MADE some 10-6s in .357 on special order, I believe it was to the New York State Police if memory serves.

I was surprised too, I honestly wasn’t expecting it but, assuming I uploaded them correctly, here are some screen shots of the email thread if anyone doubts it:

770F533C-ECED-4080-A9D8-48C700581488.jpg

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63BF0D81-EB48-4563-8D2F-43231B874B3B.jpg

Edit to add: I went on to ask them to answer the ammo part of my question but they just said they do not manufacture ammo and to ask SAAMI.

The problem is, we don't know and they didn't say when they started equal heat treating for the .38 and .357!

Because I know all S&W cyls were heat treated starting in 1920, but by 1945 they began using much improved steel and stated at that time, only magnum cyls continued to be heat treated.

So the next question for S&W is when did they start heat treating both?

It may have been as far back as 1955-56 when the first Model 19s were produced, the first .357s in the K frame. But then again, it may not have been.

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Jim
S&WCA #819

Well it would make sense that with modern manufacturing techniques and machine tools and the advent of a vast variety of carbides and such. Back in the day it probably would have been more economical to only heat treat the magnum cylinders and omit the process on the 38 cylinders. With modern processes you could send out an entire batch of cylinders and machine to suit as demand saw fit.

S&W advises that model marked K frames are OK with +P ammo. This started in 1957, about the time .357 K frames were introduced. You don’t have to be a rocket scientist to conclude that’s when all K frame .38 and .357 cyls were made of the same steel and received the same heat treatment.