BTW, I owned a Security Six in stainless at one time. Nice gun, strongly built, K frame weight, but the thing had terrible muzzle climb with hot loads, hurt the hand. It was no lighter than my M19 I had at the time, but the 19 was much more a pleasure to shoot, much as with the Taurus 66s. It wasn't terribly accurate with .38s either an dI shoot a lot of .38 brass, cheaper to get than .357 brass and helps me pick my light loads out of my heavy. There's one at a pawn shop near me now. It's pristine, nice gun, but they want $400 for it. That gun hasn't been built in 20 years! Some folks think the Security Six is the best revolver ever built, but it had its flaws, too. The GP100 addresses some of those flaws and beefs up the basic design, but at the price of weight. The things are awfully heavy to have to tote all day. To me, K frame guns are the best compromise in weight vs strength. No, you probably shouldn't put 200 rounds a day of 125 grain full house .357 through it, but from what I've seen, the gun will outlast the owner in normal use. The guns are stronger than most detractors would have you believe. The ones that got the bad rap were used heavily in police service. Those guns, used for training and such, probably fired more rounds in a week that I feed mine in 10 years. With a 100 percent diet of hot loads, stands to reason they'd get loose in five or 10 years.
I've stopped worrying about the strength of medium weight .357 revolvers like the M66. To me, it's a non-issue, but I'd rather tote my .45 Colt Blackhawk around all day than a GP100, the thing isn't any heavier! There are lighter Smith and Wesson L frames out now, designed for carry. That's an option if you don't like the K frames, but the M66 is a great gun and I found mine for a lot more attractive pricing. My 4" is like new, slick, accurate, tight, not more than 10 or 12 years old, and I bought it used for $197. I think I'd have to be on crack to pay $400 for a 20 year old Ruger Security Six, considering.