Gibson.... Thanks for the dope on WC 820. But "15.25 grains?" How do you measure powder to 1/100 grain?!!! Man, you got to be the PUMPIN IRON SCIENTIST.
A few notes on .41 frame double actions (Colt Python, S&W M586/686, GP 100):
* After sending a Model 19 back to S&W three times, the test lab at Speer in Lewiston, Idaho replaced it with a Security-Six. Thirty thousand rounds later, the Ruger had not broken down. I would expect severe forcing cone erosion. (Why any ammo lab would use an M-19 for testing .357 mag ammo is a mystery only only a sadist could explain.)
* To test a Security-Six, Ruger screwed in a barrel, which they neglected to drill & rifle. A .357 Magnum fired into the solid barrel departed the cylinder/barrel gap in terrific sideblast. Otherwise, didn't do the gun diddly. I didn't see it; was told so from the very top.
I may be wrong, but the "barrel stub" poking through the barrel socket into the .41 frame does not permit the thick ring of steel around the forcing cone of a .44 frame. It should be better than on a .38 frame, but this isn't always true.
In silhouette, a Python in the hands of Jerry Moran of Michigan, Allen Kirschner of South Carolina, Philip Braux of Louisiana, and others, established in no uncertain terms the credentials of that revolver. Eventually, guns with a thin barrel throat may crack the barrel through the forcing cone most often at 6 o'clock. (Jerry Moran loaded the Sierra .357 170 FMJ over 296; don't know what others loaded. Moran was not a Rocks & Dynamite silhouetter. He's one of the great Python mechanics and did his steel shooting with a blue 6" Python.)
I don't know much about the GP 100, other than rugged design. I would guess that its first place of wear-through might be the barrel throat. If you recover bullets fired into snow this winter, you'll have an link in the puzzle of how your bullet responds to that powder/pressure, and whether your bullet made a pristine leap from chamber to rifling.
All the best,
David Bradshaw