I've been enjoying a couple of Ruger 5" blued GP100s, one in .44 Special and one (to a far lesser degree, since I didn't stock up before the latest ammo market rollercoaster) in .327 Federal Mag.

I don't know that it'll go anywhere, but I've been bugging Lipsey's to commission runs in .22LR (yes, even with the recent troubles normal GP100s in .22LR have been having over the past couple of years) and 9mm.

The question flitting through my head at the moment is this: If Ruger made one of those in 9mm, is there anything they would have to do in order to make both 9mm and .38 Super work in the same revolver besides simply not shortening the cylinder?

I understand that technically the .38 is supposed to be a .356" rather than the 9mm's nominal .355", but it seems to me that current manufacturers of the ammo are loading the .38 with .355" bullets anyway. My guess is that there's ample room in the cylinder for the semi-rimmed .38 Super case. Per SAAMI, both have rim thicknesses of .05" (more or less), although the extractor cut for the 9mm is nominally .035" versus the .38 Super's .04". (see http://saami.org/wp-content/up...-14-Posting-Copy.pdf )

Generally, (but not always) to use a autoloading cartridge (rimless or semi rimmed) in a double action revolver, you will need to use moon clips of some sort.
I guess you could swing the cylinder open and poke the empties out with a pencil or dowel if that's what you wanted.

There have been several double action revolvers manufactured that have special "extractor stars" that overcome this basic problem. (added little mechanical fingers/widgets)

Single action revolvers do not have this problem with extraction as each fired case is extracted manually.
I found a blued Ruger Blackhawk 9mm cylinder and fit it to a stainless Ruger Blackhawk chambered for .357 Mag /.38 Special.
I sent the blued cylinder out for milspec parkerizing after the cylinder fitting & test firing was completed.
(I also fitted a high polish stainless "Birdshead" grip frame with Micarta grips)
It doesn't seem to matter 0.355"/0.356" as it shoots both diameters well.

I never shoot .38 Special or .357 Magnum anymore.

IMG_20201209_145418094 by cee_Kamp 32ACP, on Flickr

I'm not certain, but memory says 9mm is a tapered case, and .38 Super is a straight walled case. There is also a considerable OAL difference.
So it's quite possible that two different cylinders would be required for the dual caliber setup you are thinking about.
A 9mm will likely drop too deep in a .38 Super chamber and won't fire in a double action gun without moon clips.

It would be much easier to go with a single action.
OEM in .38 Special /.357 Magnum.
Locate two 9 mm cylinders and have one reamed to .38 Super.
Then it's four different cartridges.

Ruger sells several Blackhawk Models with two cylinders.
.38 Special /.357 Mag in one cylinder.
9mm in the second cylinder.
Buy another 9mm cylinder and have it reamed for .38 Super.
Ruger won't do that, you will have to seek aftermarket services.
Blued & Stainless, two barrel lengths: https://ruger.com/products/new...vertible/models.html

I think Ruger could easily do a 9MM GP100, that could also accommodate .38 Super, if they perceived such a revolver would sell in adequate quantities. The SAAMI spec for 9MM, 38 Super, 9X23 Win., .38 Special, and .357 Magnum bores is the same. I have used jacketed .357 bullets in 9MM pistols, and jacketed .354"-.357" bullets in 9MMs and .38 Supers without issue. I suspect manufacturers use a common bore size for their .38 and 9MM guns, and that tiny assumed .001" difference between 9MM and .38 Super bores may not be a reality. According to Brian Pierce, writing in Handgunner, most manufacturers are using .355" groove diameters for both their 9MM and .38 Super pistols.

A more noticeable consideration might be the different case head diameters of 9MM and .38 Super. But I don't consider that much of a problem either. My 38 Super pistols handle both the straight walled 38 Super, and tapered case 9X23 Winchester interchangeably, and without issue.

I currently have a S&W .357 cylinder out for conversion to 9MM. The gunsmith indicates the cylinder will also allow use of .38 Super. So, while moon clips would be required for easy extraction, IMHO Ruger could do a 9MM GP100, that could also accommodate 38 Super, if they chose to.....ymmv

FWIW, existing Ruger 9mm revolvers use moon clips, so I guess I just assumed the pistol I had in mind would as well.

Love my Ruger Convertibles! Being able to shoot .45ACP is way cheaper than .45LC. I also have the .357/9mm model.

Although you may quibble over tapered rimless vs straight semirimmed, they will both shoot in a compromise chamber.

Pinnacle will cheerfully cut that compromise chamber in a .357 cylinder.
https://pinnaclehighperformance.com/cylinder-work

That would be more productive than waiting for Lipsey to tell Ruger to make one for you.

^^ Now there's an interesting thought. To this day, IIRC, Ruger still uses the same barrels for .357/.38 revolvers and 9mm revolvers. I'm not sure how easy it'll be to find the donor I'm looking for, but I'll shoot those guys an email and see what they say.

My 627 PC was made for .38 Super; Randy Lee converted it somehow so it shoots 9 mm and that's what I shoot most all the time (with moon clips of course).