I can't speak to the 44's, but the 66 I have alot of time behind. I have fired tens of thousands of rounds through various model 66's in different barrel lenghts. Thousands of those rounds being 158 grain 357 and thousands being 125 grain and 110 grain 357. Lots of 110 grain 38+P+ as well.
I've yet to shoot one loose, break a forcing cone, stretch a top strap or suffer any of the other various maladies attributed to K-frame magnums on the internet. For years on this and other gunboards I posted asking for anyone who had a 66 damaged from use to please post. In over eight years I only had one taker. A fellow here posted a photo of a cracked forcing cone on a 66. Only one of a 66 I've seen in over 42 years of shooting K-frame magnums. So, it has happened. So what?
"...shot nothing but 357 full loads in his 66 for over 15 years.." This. The only thing amazing about this statement, to me, is that the poster evidently feels this in in some way insufficient service life. I'd wager that the majority of folks on this board probably don't shoot that many rounds in ten years through ALL their guns, let alone a single example. My high round count 66 is a former Chicago PD 4" 66-2 duty gun with over 25000 rounds through it. The retired Chicago detective I purchased it from told me he had shot well over have of those using 125 grain 357. This 66 shows some forcing cone erosion and a little endshake. Its slow to carry up on one chamber too. It is also my most accurate revolver, out shooting my various Performance Center guns. One expert shooter I know, who has fired it numerous times has pronounced it to be; "..a sub 1" gun..". He constantly badgers me to sell it to him - warts and all.
Anyone else ever notice that it is usually the same people on the internet cautioning folks about the alleged "weakness" of K-frame magnums? Makes me wonder whether they have actually ever owned or shot one, or are just passing on what they read elsewhere.
If these revolvers were as delicate as I read on different boards, I'd have seen more failures than one gun. Hell, I've personally seen three wind up revolvers locked up tight during the last ten years alone. And I'm told here; "thats not an issue"
So, I will continue to enjoy shooting and competing with my pre lock model 66's as well as all my K-frame magnums. They remain the finest revolvers to ever come out of S&W and judging from the current line up of products coming from the company calling itself S&W, its unlikely they will be surpassed.
Just for grins, next time some "expert" is lecturing you on how "weak your K-frame" is, and how "the L-frame was made to replace the K-frame", ask them why S&W continued to make K-frame magnums right alongside L-frames - FOR THIRTY MORE YEARS??? They love it when you do that.

Regards 18DAI