Cornish X (the usual meatbird) are hybrids, meaning their parents are not cornish crosses. They use a cornish and a white rock, I think, although my memory is very fallible on this point. Even if you manage to raise the cornish x's to laying age, which some people report they have, they will not lay eggs that will hatch to be cornish x's. Also, I'm not sure whether the roosters would be able to fertilize the eggs due to their weight issues (like some commercial breeds of turkeys that have to be artificially inseminated because they are too large to mount a hen).