From what I've seen the -3 610's were a real mixed bag in concern to fluted cylinders. Every 6 1/2 inch -3 I've seen has fluted cylinders but with the 4 inch version it seems that S&W started building them using cylinders left over from the prior production run. Later on the 4 inch version got fluted cylinders, which I strongly prefer.

One model that I really wish they had made is a 610 Mountain Gun with a tapered semi lugged barrel. Who knows, with S&W anything is possible, next time they re-issue the 610 maybe a distributor such as Lipsey's will order up a batch of 610 Mountain Guns. If so, I hope they insist on a properly roll stamped barrel, the laser etching they put on the 686 Mountain Gun was IMO too gaudy and in poor taste for such a fine revolver.