A two time NRA Bullseye Pistol Champ, and 10 times PPC National Champ told me his K frame 38 Special has around 600,000 rounds through the shilen barrel and still prints 2 inches at 50 yards. I did not ask if it was a 38 Special or 357 cylinder, probably a 38 Special. He fired a 148 LWC with 2.7 grains Bullseye as his competition round. Bud says he had a firing pin break, the cylinder ratchet wore out. He sent it back to S&W for retiming. You shoot light loads in a S&W and they will last an incredible amount of time. Bud says when shooting in competition that required "major" loads, he had a forcing cone crack. I think that is the primary reason for the M686 introduction, shooters were firing a lot of full power 357 loads. He also said that he saw only one individual shooting a Colt, because Colts got out of time faster than S&W's. The Colt locks up just as the hammer falls. A little wear in the cylinder hand or ratchet, and it is out of time. The S&W locks up prior to hammer fall. Colts barrels were tighter, and more accurate than the S&W's, so bud said that some competitors had Colt barrels installed on their K frames, and the pistols were called Smolts.
When the M19 or M66 was designed, it was built on the standard 38 Special frame and extensive practice firing was understood to be 38 Special loads. Full power loads were more or less reserved for occasional use. Few shooters back then had the crazy round counts of recent shooters.
Bill Jordan was the main proponent of the pistol. Bill was a Border Patrol Officer and I am certain out in the hot, dry, of the Southwest, he wanted something somewhat smaller than a bowling ball on his Sam Browne belt! I assume there were differences in the heat treatment of the receivers, but, don't know. Might have been differences in forcing cone angles, cylinder mouths, don't know.
My Python is a safe Queen. When prices got too high, I stopped shooting it.
I do have a Colt MKIII which shoots way too high, and I can't find a drop in taller front sight. That is one of the problems with these out of production pistols. Parts are non existent.
I shot a M66-1 to where it was slighly out of time on one or two cylinders, and traded it in, with some boot, for this
As I have gotten older, I don't care for the blast or recoil anymore. It takes too long to get rid of the flinch, so I have been downloading my cartridges. I do not like cleaning out the lead ring that developed in the cylinder from shooting 38 Specials, so I went out and developed 38 Special equivalent loads in the M66 and MKIII. The pistols ought to last forever with these loads.