Floating a barrel doesn't always improve accuracy with any rifle. In any case, like corney says, Cooey 64's aren't known for great accuracy. Sometimes using a torque wrench on the stock screw can help, but that's a trial and error thing. The front screw goes into the receiver, not the barrel. You could remove(use sand paper) some of the wood in the barrel channel, but it may not make any difference.
You'd be better off trying as many brands of ammo as you can to find the one or two that your rifle shoots best.