I have some Dark Cornish and the ladies are getting nice and chunky but the Roos just don't seem to be filling out as well. Does anyone know if this is common? They are hatchery as that is all I could find at the time. Thanks!
Give them time, they do not really fill out until 24-26 weeks. They don't really look like much until their first molt either, however after that molt they are very pretty birds... one of my favorites to look at. But, I also had hatchery stock, and they didn't get any thicker than the white rocks I was raising at the same time.... so it's hard to say.
I have seen some good stock on this site though which didn't resemble my DC at all. They looked like a colored cornish x rock as they were so compact. Try finding someone on here with good stock to better your existing lines.
The DC Roosters do take awhile to fill in as opposed to the hens, and hatchery stock is even a little slower and not as big & broad as they are bred for egg laying. Outcrossing with some bigger/better stock should go a long way in helping your DC flock bulk up.