I just bought a Schultz and Larson in this chambering with a 26" barrel. I used John B.'s data from Gun Gack 1 which was 53gn H4831 with a 140gn bullet for 2930/2940 fps (26"). My rifle gave 2885 fps with the 140gn Hornady Interlock (26"). I'd be very surprised if you got 2850 fps in a 20 inch barrel. I'm not sure the conversion would be worthwhile in that barrel length. But good luck.
