I have a old revolver that says pat. May 22 1917. On the barrel it says

FOR >38 L Colt<CTGS
38 S&W Special

Wondering what it will shoot.
I bought a box of 38 long colt 158 grain ammo. But wasn't sure if it shot smokeless powder

Welcome to the Forum.

It sounds like you have a Smith & Wesson copy. Please post pictures.

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John 3:16
WAR EAGLE!

What Muley said.

If it has a patent date of 1917 and it actually says .38 S&W Special on the gun, it is at least THEORETICALLY designed for use with smokeless powder, since that caliber was commonly sold only as smokeless ammunition within just a few years of its introduction in 1899.

But it does indeed appear not to be a Smith & Wesson, so how safe it is is a different question.

"it is at least THEORETICALLY designed for use with smokeless powder, since that caliber was commonly sold only as smokeless ammunition within just a few years of its introduction in 1899. "

I have no idea who the customers were or how much was sold, but the .38 S&W Special remained available in factory BP loadings until the mid-1930s with approximately the same ballistics as standard smokeless loads.

Well, yes, UMC actually catalogued it until 1939, but that doesn't mean it is a reasonable assumption that a gun from 1917 or later would be designed for BP only.