I have the 7X307 and the 6X307, for the Contender, and the 6.5X444 for the Encore, I'm guessing yours is 444 cut to 307 length, full length 444 would be too much pressure for a Contender. Don Bower did my work, he and the other guy were friendly competitors. Think JD Jones wildcats are pretty much the same idea.
Your barrel should be capable of better groups, I've done that good @ 500m with all my barrels, not consistantly, but enough to give me hope. Probably the most knowledgeble guy I know on the subject would be Ladobe here, 500m is childs' play for him.
Good Luck, Jim