I'll assume that your looking for a new gun to purchase.
If so, the model 66 has been discontinued. It's replacement in the line is the L frame model 620 which uses a 2 piece suspended barrel. That is a barrel under tension with an outer shroud surrounding the barrel. The barrel is produced with a cap on the end and, when inserted into the shroud and torqued into the frame, the result is a barrel that is under tension between the cap on the end of the barrel, the shroud, and the frame. Dan Wesson revolvers used a similar approach and they are famous for their accuracy. Which is one reason why I chose to purchase a 620 instead of the more common 686, the other reason being that I like the look of a half lug revolver more than a full lug style like the 686. As for it's accuracy, this week I managed to produce a 3 shot cloverleaf at 40 feet that I could cover with a dime. However, I was cheating by doing that in single action and shooting off the bench.
So, now you have 2 choices for the L frame stainless steel S&W revolvers, the 620 and the 686. In terms of handling they are both nearly identical, which means they are a bit barrel heavy and both weigh in at about 38 ounces. I also have an older model 67, which is the model 66's 38 caliber near twin. Pluses for the older K frames is that they feel very nimble in the hand. Basically, the K frames are like a good small sports car like the Mazda Miata or the Cooper S, the L frames are a bit like a good sports sedan, say a BMW 635. Then there is the N frame 627, which I would consider as the equivalent of a good Mercedes S series sedan.
Now, if you have no problems with buying a used revolver, AND, won't abuse it by shooting a lot of full power Magnums at the range, the absolute best choice you could make is the model 66. Frankly, I think that S&W was nuts to stop making the model 66. In terms of handling qualities it's hard to beat the K frame, they have superb balance and are quite easy to change point of aim with quickly. However, history has shown that a steady diet of full power Magnums really is too much for the K frames and the Lawyers have had their say. So, you can only find them used and you'll pay almost as much for a used model 66 in very good condition as you will for a brand new 620 or 686. You will also find it quite difficult to find any used model 66 for sale unless you hit one of the auction sites such as gunbroker or get really lucky. What I am saying here is, if you happen on a model 66 in good condition, BUY IT, you'll always be able to get your money back. However, I won't purchase any revolver that I can't check our carefully with my own hands and I have yet to see one single model 66 for sale locally.
Now a word bout grips. One great thing about any revolver is that yoou can purchase grips so that the gun fits YOUR hand. The current 620 and 686 use a grip that I found to be way too small for shooting full power Magnums with. So, my 620 wears a grip that was originally produced for the 500 Magnum. Point here is that you will want to plan on doing some grip shopping. Ask any long term revolver shooter and they can probably show you a drawer full of grips. Once you've purchased your choice, just try and identify what you need in terms of grip improvement and ask here. It's what I did when I got my 620 and the advice I received was spot on perfect.
