midtncattle, I've never raised any Charolais, but our red simmi's fall right in the same pen with them at the sale auction. Generally from what I've seen the Simmental is a little shorter in the frame or leg but thicker across the back and a little more depth. Biggest difference I have seen is better dispositions, and a darker calf. I would think the Black Simmental birth weights are smaller, but again I haven't raised any Charolais. I know this guy has really shocked me a bit on his bw's, I've had 60 to low 70 lb bulls, but they really grow. His calves has lower bw's than our high CE Dream On son did.
Glacierridge, I only took 1 pic of him real quick but if I take the camera back with me to the pasture I'll get you a rump shot.