My Cooper .17 MACH IV never liked 25 gr V-Max bullets either....probably to do with the twist rate vs the longer V-Max (higher BC) bullet?
About the same response for 40 gr V-Max .20 caliber bullets in my Cooper .204 Ruger....doesn't shoot them well vs lighter bullets.
I suspect that this is the issue, long bullet twist.
Mine shoots 20 grain VMax very well.
