The 'massive looking' 4" Ruger GP-100 weighs 41 oz, while the six-shot 686 weighs 1.3 oz less. Put a seventh hole in the 686 to make it a plus (7-shooter) and you pare away an additional 0.8 oz. The extra 'mass' in the GP-100 is easily found - look at that shroud vs S&W's full lug. I'll take the S&W's hammer forged and heat-treated frame, etc, over the Ruger's cast steel, too. One time the GP-100 QC was horrible - it seems far better now. Still, buy as 'much' revolver as you can afford.
In S&W's current standard production offerings in the 4" barrel, they start at the 620 and end with the 627 Pro at about $120 more at a fair dealer. That buys you a lot more revolver, too, as I found out when I went to my dealer's last spring to buy a 4" .357M 7-shooter 620 and came home with the 627 Pro 8-shooter N-frame. I now rate that as one of my two best-ever S&W 'buys'.
Get the 4" .357M first - it will help you develop your shooting skills as a great plinker, while doing double duty as a home defender. Add a 642 Airweight in .38 Special +P and you'll have a great CCW - a totally different 'animal'. The right tool for the right job. Don't let anyone fool you - .38 Specials - especially +P rated like the venerable 'FBI load', the 158gr LSWC(HP), or the short-barrel-designed Speer 135gr Gold Dots - are perfect protection, in the home or car or on your person.
Stainz
PS A new S&W connects you, via an 800# call, to a lifetime warranty, too, should you ever need it.