As has been suggested make sure scope and mounts are tight.
Are you using a scope that you have personally shot groups of less than 1" @ 100 yds. with?
Have you established what the throat is on this rifle? Perhaps working with some OAL's would bring some results.
Although a Cooper should put anything into an inch or less, as long as the weight matches up with your twist, and it sounds like your good there.
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