I have another question for you. Really I'm not trying to be a smarta** , I'm trying to understand. Aren't the Cornish rock x the quintessential meat bird? If so, how is it that they can lay a huge egg, but the Cornish breed can't? Is the cornish breed structurally very different from the cornish x? Maybe that's my confusion? I've been thinking if the cornish x can, why not the pure cornish.
Or, maybe the cornish x can't - Does laying that huge egg eventually kill the cornish rock x, if it doesn't die from something else? (I know that it's a terminal cross in that they have very short lifespans- but I do read that some people have been successful keeping them to laying age).
Likewise, these birds aren't bred to lay either. yes, they'll lay large eggs, of course, they'll also lay small ones, and flat ones, and round ones, and double yolked ones, and even triple yolked ones. they'll lay an egg of every shape and size, and every kind of yolk. Most will be infertile, but a few will be fertile, and even fewer viable enough to hatch. Laying these completely different eggs, is what sometimes will kill them from being egg bound.
In my projects using CX birds, I got really poor laying- even poorer than the Cornish. Really erratic laying, eggs of all sizes, shapes, and when the entire thing was over, from the 5 pullets I kept to experiment with, I ended up with 2 cockerels. Those 2 cockerels made the entire thing worthwhile--- but point is... comparing anything to CX laying, or eggs, is really a poor comparison.