I know the gun is going back but this can be info for other wolverine r owners. A reason for the stiff cocking is an over/wrong adjustment of the trigger. I had this with my wolverine when adjusting it. In my experience one of the grub screws would move after adjusting during shooting and the lever would get stiffer and stiffer to cock. Put some blue loctite on the grub screw and never had bother again.
I will do my best to give more detail/update as to which grub screw it was when my memory gets jogged
