The trouble with breeding a Cornish X is that they are already a hybrid. Anything you breed with them is gonna be like a X X or something
If I were you, I would eat the 12 week old Cornish X's that you kept, and try breeding different chickens. Here is the meat bird thread I think was alluded to earlier:
https://www.backyardchickens.com/forum/viewtopic.php?id=64055

If I were you, I would eat the 12 week old Cornish X's that you kept, and try breeding different chickens. Here is the meat bird thread I think was alluded to earlier:
https://www.backyardchickens.com/forum/viewtopic.php?id=64055