Was recently given an old K 38, 49,xxx. Has a buldge in the barrel about 3” forward of the frame and an operation number engraved on the side plate along with some pitting on the cylinder.

Would like to convert the gun to 9mm with a 4” barrel. Anyone see any issues doing a cylinder conversion?

I would say not to do this. First off a 9mm offers only marginal differences in stopping power (if using the right 38 Spl. load). Secondly, I believe the .38 Spl. is inherently a bit more accurate. Thirdly - why invite extraction issues with a rimless cartridge? Personally I see no real upside and plenty of downsides - but that's just the skepticism in me. There should be replacement barrels available for your original caliber and you can at least have the original configuration and styling - but that's your choice obviously.

All that said..... as long as a qualified GS tells you it is safe to shoot - see how it works without doing anything. Since it's no showpiece it may just fit the "plinker / knock around gun" slot in your collection. Yes, many times a bulge is "curtains" but sometimes it doesn't affect things that much.

I doubt it pays to have a new side-plate refit, re-blued and of course change the barrel too, so it may just pay to use as is if safe of course.

Unless you can do quality work yourself, these conversions are usually expensive beyond any logical gain in utility. I say this not to discourage you, but just to make a point of it. Good quality revolver work requires not just machining skill. It takes an eye for detail and style based on knowledge and experience. Folks with this capability rarely work cheap.

If you really want a 9mm K-frame revolver, you might just look for a 547. It will cost some money, but when you are done with it you should recover most or all of your money, if not more. With a frankengun, odds of breaking even aren’t good.

I agree with just putting another barrel on the gun and calling it a day. All this JMHO - based on experience.

I am going the other direction, enabler that I am. I have a Model 10 round butt that I got with issues. I replaced the barrel with a 3" and found another cylinder. I did some careful work with a range rod and found that the new 2 me cylinder lined up with simple replacement of the cylinder and ejector rod. I sent the new 2 me cylinder to Pinnacle Gunsmithing (look it up on Google). He cut the cylinder for moon clips in 9mm. I now have a weapon capable of firing both cartridges with the 2 cylinders by dropping one screw and replacing the cylinder. Until recently, 9mm was the cheapest centerfire defense cartridge. The barrels used by S&W for both cartridges are internally the same and the .357 lands catch and spin the .355 bullet although not as deeply. I have recovered and examined bullets fired from my gun. The new Speer Gold Dot, Hornaday Critical Defense, etc. 124 gr 9mm are very effective in LE testing. All in all, I have $300 in this effective 2 caliber defense gun. Although it is not pretty, you don't want me shooting at you with either cylinder installed. BTW, can anyone change this jpg file so it will enlarge? OK, redid photos

Attached Images

	20 12 26 Mod 10 3 inch loaded 38 & 9mm cylinders.jpg (56.1 KB, 32 views)
	20 12 26 side view 9mm & 38 cylinders.jpg (66.0 KB, 35 views)

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SWCA 3417 HF 642 NRA-TC

Have you shot this one yet? Many revolvers with bulged barrels shoot just fine.

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John 3:16
WAR EAGLE!

I made several of my J&G gunsmith special 10-7s into 357s or 327s.
I am going to ream a couple of the left over 38 special cylinders to 9mm and shave them for moon clips. Not only do you have to ream the cylinder, but you have to remove material from the rear face for the clips and that includes a bit of scallop between the ratchet teeth.

Here is something to think about. The cost of clips, only place I can find them is TK Custom 10 for $70, which is way spendy compared to 45 clips.n $7 a piece.

TK will ream and recess your cylinder and sent you 10 clips and a clip loading tool for $340. They also state in big bold red letters that this is only for standard pressure 9mms
S&W Firearms Revolver Cylinder Machining - TK Custom

I am only doing it because I can do it for the cost of renting the reamer. I currently have nothing that will fire 9mm ammo. I already bought 10 clips and use a couple of them to shoot 22TCM in a cylinder that shares a frame with a 22 Harvey Kay Chuck cylinder.

You might not want to do it in that old of a gun. Metal strengthening (and all that stuff I'm not well-versed in) back then was not what it is these days. Now, if you had one from the modern model-numbered era, then no problem.

I am one that is always for conversions. If the factory does not make what you want, then make it yourself.

Do we really care how much profit we make or do not make 10 or 20 or 30 years down the road on a single firearm?

However, a pre-1957 cylinder may not be up to the task of containing the 9MM Parabellum's pressure. We are taking about more than double that of a 38 Special

In this case, I do not believe this firearm is a good donor for this project

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"Acta non verba"

That early a K38 probably has a lighter weight, narrow rib barrel... it is probably worthy of saving, using an original early type barrel rather than making the kind of mods you are proposing. This coming from a guy who has done a couple of conversions of this sort. Nine mm revolvers and later 38s suitable to make these conversions are relatively common and available. I’m not against the conversion, just the proposed donor gun being used. Then again, it’s your gun, so it’s your decision.

Froggie