Your question is predicated upon your having read/heard a certain datum - - -
Can S&W L-Frames really not withstand a steady diet of FACTORY (not extra-hot handloads) .357 magnums without losing their timing or having some other problem?
May one ask where you got this? S&W supposedly introduced the L frame because K frame .357s had trouble with a steady diet of full magnum loads. The L frame is generally considered to be about as strong as the Colt Python and Mark III Trooper, without being as heavy to carry as the S&W N-frames.
I keep reading that Rugers are stronger, but have never heard of someone messing up their S&W K or larger frame with .357's.
No question about it: Rugers are indeed strong revolvers, possibly the "strongest" service type revolvers, from the standpoint of longevity in shooting heavy loads. The early Ruger DA .357s, the Security Six series, were probably about the equal of the S&W L frame in strength. The later GP series were probably the equal of the N frame, with sturdier lockwork.
The S&W K frame magnum, the Model 19 Combat Magnum, was introduced back in the day when a lot of people, cops especially, qualified with .38 Spl loads and carried magnums on duty. A model 19 lasted indefinitely with this kind of practice. When agencies had cops start qualifying with magnum loads, it made sense that this steady diet would loosen up the K frames quicker, develop end shake, and the like.
Another factor was issuance of the 125 gr JHP .357 loads. It appeared that the lighter framed mags, models 19, 13, 66, 65 - - suffered flame cutting with these loads. S&W saw an excuse to introduce a near-duplicate of the justly famed Colt Python, complete with the full length underbarrel lug. Heavier revolver - -More comfortable to shoot - -more inertia to slow down the acceleration during recoil - -and, best of all, S&W could sell the L frame for less money than Colt's could sell the Big Snake, and so regain some of that market share.
Personally, I'd hate to pay for the amount of FACTORY ammo it would take to ruin my Model 19. Let's see - - Speer Gold Dot JHP 158 mags sell locally for about $13 for 20 rounds, or $65/100. Find a deal on them by the case, and you still pay at least $500 per thousand. How long it takes to loosen up a K frame? I'd think it would take at least $1,000 to shoot loose a K-frame with factory loads. I can't afford it - perhaps you can. And, it only makes sense that an L frame would last longer than the M19.
And then there's the wear and tear on my hands. About 50 rounds per range session is all the full magnum loads I enjoy. I shoot mainly because I like to. Happily, I choose to carry a .45. My magnum revolvers are mainly for fun, though I do qualify with them, just for fun.
No, sir - - There a lot of things I worry about in life, but wearing out a magnum shooting factory loads is not one of them.
Best,
Johnny