Yeah, I'd go back and buy a couple more boxes of that CoreLokt. After you've sighted in about two inches high at 100 yards (dead-on at 200, six inches low at 300), I'd try offhand beer-canning at around 100 yards.
Use up at least a box, in that practice. There's nothing written that you can't shoot once or twice or so, and then take a break for a Coke or a cuppa jamoke. You don't have to beat yourself to death.
, Art