Here's a cornish cross next to the same bantam and box graphic
10 days later, here's a picture of a buff orpington chick and a cornish cross chick. Click on the picture for a bigger version. Notice the foot size on the cornish.
We raise both cornish cross and heritage breeds. As far as eating, I prefer the heritage breeds, but some of our customers want the cornish, so we raise a few batches of them over the course of the year. They do pretty well to supply the demand while the heritage are growing out. This particular chick will be processed in 40 days, at about 6lbs live weight.
In a mixed brooder, you can tell which chickens are the cornish from the first day. They're the chicks that fall asleep with their head stuck in the feeder. The leghorns are the ones that run screaming from you when you feed them. The buff orpington chicks are calmer.