depending on the breed you can usually tell if a steer is finished by looking at the brisket. should be full or heavy looking. a sure fire way is to see a fat pocket develop at the tail head section of the calf. the topline of the calf should be flat with a dimple appearing at the middle of the backline. sides of the calf along the ribs and rear quarters should be dimpled. at the moment i have two steers and a heifer that weigh about 1000 lbs. and are eating 20#/day. they are pretty much on full feed. they're getting corn, ddg's and soyhulls at about a 10.5% protien level, plus all the hay they care to eat. the heifer should finish out between 1150 and 1200 lsb. , steers should finish out between 1300 and 1350 lbs. i say that from past experience with my own animals, knowing there genetics, frame size and feed schedule. yours will probable be different. imo there's nothing magic about 1200 lbs.
ROB