The guns shoot that well, and I'm glad to see a competent marksman post a group here that reflects it. Some on the Net post groups that I'd be embarrassed to admit that I'd shot. Some of those targets are shot at disgustingly close range.
And, yes, they will do that with full .357 ammo. Probably not with those awful lead loads, but they shouldn't be used, ever, anyway, if still made. They'll lead plate your bore in short order.
But the better JHP 357 ammo is extremely accurate. I've fired some lots of older Remington 158 grain JSP and JHP that were just remarkable, and some Federal equivalents were also outstanding.
The Ruger GP-100 is also very accurate. Mine shot groups fully on par with what a M-686 (both with four-inch barrels) would deliver. The S&W did have a lighter SA trigger pull, which helped it to shoot well, but my Ruger's trigger is also pretty good. I eventually sold the S&W, which says a lot for how I feel about the GP-100. The balance of the 686 just was too nose-heavy for my preferences. Others may like that.
I have yet to fire an S&W revolver that would not shoot beyond my capabilities, and really talented marksmen have told me the same. But groups like that shown can be achieved at least occasionally even by those of us who aren't of Olympic quality.
And they can be fired while standing on our hind legs and shooting with one hand. Sometimes, on a good day...
To be sure, if you can sit and fire two-handed, the better groups will be seen more often. But the guns and the right ammo will do their part.
Are those powder burns on that target? 
More likely 20 inches!! 
