A lot gives... Weather, surroundings, feed, water is just a start...
What percentage feed did you feed them?
Did you have them outside?
Was the weather cool? 50 or below?
Crowded? or Did they have too much room to run?
Cornish x need to have at least a 20% protein to preform well and the weather needs to be somewhat stable without huge fluctuations. If you have them running free range they burn a lot of calories and naturally are going to take 9 weeks to fill out. If they were crowded too much their growth will be stunted to the point of a 5 week old cornish and not much more.
All of these things will delay you a week or even two in processed weights.
In 6 weeks you should have a bird that is 3.5 lbs dressed weight. So if you have birds averaging 4 pounds you are in the right direction and you did things right. Your not going to get 10-14 pounders in 7 weeks or even 8 weeks. It normaly takes at least 10 weeks to achieve birds of this stature.... which honestly its luck of the draw, as most hatcheries have a pot luck on what line of chicks they hatch. Some are roaster strains which will get a lot bigger than a fryer strain with few problems. Some are cornish x hen strains and are designed to live 5 weeks and only be a pound and a quarter dressed.
Too many factors play into why your birds aren't what you expected.
What were your average weights?
