Maybe we could work something out :D
I'm in the same boat going the other direction
https://www.northwestfirearms.com/threads/ruger-american-rimfire-standard-for-compact-modules.369623/
IIRC John Taffin wrote an article about a gun like this made by (again, IIRC) Bill Grover of Texas Longhorn Arms. He had made the barrels and cylinders different lengths with the 44 cylinder being the longest and the smallest bore having the longest shank. That way you might be able to...
Not only do K frame holsters work perfectly, but you can usually find used K frame holsters for a fraction of what you would pay for an identical holster marked for a Ruger "Six"
I think you will find the same issue with S&W K vs L frames. I'm in the same camp as you silverback, and my best guess is that it is because the bore axis of the GP100 / L frame is higher than on the 6 / K frames and that results in more upward twist.
I know this is an old thread, but I was clearing out some old boxes the other day and found my receipt from about 15 years ago when I very briefly owned a 6" half lug GP100. I know that the weight is supposed to make the GP100 a softer shooting gun, but for me in my hand the tiny bit higher...