I've been testing a variety of handloads in my .357 blackhawk as well as a few factory loads. I decided to see what happens when I overlay a bunch of my targets. This represents 6 different handloads and 3 different factory loads. All 158 gr bullets but includes plated SWC, lead SWC, JSP, XTP, and LNHP. Velocities ranged from an average of 871 fps for my plinker loads to 1300 fps for some hotter H110 loads to over 1400 fps for AE factory loads (which surprised me they were that fast). All shots were at 15 yards indoors of a rest.

If I'm reading this right, 90% of my shots fell within a 1.81" radius or 3.62" diameter circle. In other words, regardless of load I should be able to hit a 4" circle 90% of the time indoors off a rest. Real world off-hand shooting will obviously open up more, but then again a more skilled shooter would do even better.

What software are you using to generate those statistics?

http://taran.ptosis.ch/taran.html