I have to agree with 22-rimfire. Get a 5 inch.
Since this will be a range gun, then choose a longer barrel. Even with a 4 inch barrel, the muzzle blast is noticeable from a .357 magnum. A five inch will mitigate that blast a little more and give you a slightly longer sight radius to make hitting the target a little easier. And the 5 inch is not quite as unwieldy as a 6 inch and can ride along with you in a holster while hunting without hitting you in the armpit while sitting in the truck.
The firearms distributor, davidsons, offers a 5 inch, Ruger GP 100. They seem to be in stock right now but may be allocated. I would try for one of those.
A 5 inch barrelled revolver was Skeeter Skelton's favorite length. I have a 5 inch model 27, and it will be one of the last guns I part with.
Edit: @SmithandWesson: I tired to keep my answer relatively close to your parameters, but a different suggestion came to me overnight. Since this will only be used as a target/range gun, I would suggest and smith and wesson, model 14. That is their target model, built on the smaller K frame with a 6 inch barrel, and chambered for .38 special. For your purpose, accuracy and comfort are more important criteria than power. A small charge of WW238, HP38, or bullseye behind a 148 grain wadcutter is be a delight to shoot and provides more accuracy than most of us could hope to use. The only problem is that model 14's are not in production right now, and finding a used one likely won't be easy.