they grow faster than a Ball for sure. They can vary and also depends on how regualr you get them feeding but in my experience once you get them eating they tend to stay that way providing you keep them healthy and the husbandry requirements are met consistently.
Expect your Blood to easily double its size in its 1st year, they maintain a healthy growth rate then start to fatten out.
But please dont get impatient and try to feed more food and more often, like balls they do well on a 5 to 7 day feeding cycle and fully grown only need fed every 14 days or so on a Large Rat to do well.