I don't want to sound stupid, but I bought 45 Cornish-Cross on sale at the local feed store. I raised them until 5 weeks in a brooder and then let them free range with my hens. I feed them corn, oats, and meatbird feed, as well as every kitchen scrap I come across. They are seeming to be a great backyard chicken. Everyone was telling me to butcher them before 12 weeks to assure that they don't start dying on me. However, we butchered the first 10 at 12 weeks and they were still very small and thin. We butchered the second set at 16 weeks and still didn't have anything like what you buy in the store. The last 15 are nearing 20 weeks, and are still are comparable in size to my RIR hens. They just don't seem like the "voracious eating and pooping machines" that everyone told me they would be. They have never roosted, but other than that seem to be no different than my laying hens. Did I get duped at the feed store, or am I preventing them from fattening up somehow by letting them free-range and not feeding them meatbird feed exclusively? I do leave food out 24/7, they never seem to empty feeders now that we are down to 15.