Make sure the sears aren't too worn down. Check it's well oiled and the o-rings are sticking/rubbing. There should be a screw inside the bolt for velocity, if it's a star-fire type it may not have the ball bearing to "click" at half turns.
Putting the valve on the widest port sends the most air to the velocity/bolt. Putting it on a smaller port will give you more pressure to recock.
You shouldn't need liquid CO2 but most VMs don't like HPA without some tinkering.
Two wrongs is a u-turn. It takes THREE wrongs to make a right.