Ken: with the 9mm you can get some of the 147 gn jacketed slugs out to about 1150'/sec from a 4" bbl using VihtaVuori loads and that will be sufficient for the 100 yd steel targets. From my older Lymna manual you can push the 158 gn cast slug to about 1K'/sec, which is also sufficient for the 100 yd targets. These velocities are listed for a 4" bbl so your 10" bbl should get more velocity and attendant 'smack' at the 100 yd line.
The last time I shot the 'short course' with a 9mm, as we called the 100 yd Silhouette course (way back when), you had to hit the target high to get it to topple if you were using 115-124 gn slugs - but, that could just have been me.... If you went to the 158 gn (38 roundnosed slug sized to 9mm diameters) you could hit a bit lower and get them to topple.
You just have to (1) measure your bbl for diameter and (2) find the bullet, cast or jacketed, that shoots most accurately. Whether the bullet is a standard weight 115 or 124 gn slug, or a heavier cast slug, the 9mm from a 10" bbl should topple the rams and be easy to shoot. Good luck.