rondog, I have same exact rifle and I use 19 grains of IMR 4227 behind a 255 grain Keith SWC. It's very mild and puts our smaller central Texas bucks down immediately. All bucks shot have been pass throughs with lots of internal damage and mild recoil from both my 3 screw Ruger and my 24" Rossi.
The only change I have made to my Rossi is the addition of a Lyman tang sight. Using this sight, I shot a 5 shot, < 1" group off the bench with this load at 50 yards, so I didn't experiment any further.