Here is a quick guide I recently provided a customer for tuning the FX Crown. 

The Crown is one of the easier rifles to tune. 
A chronograph is always required when properly tuning an air rifle. 

Step 1 - Select the appropriate caliber on the transfer port wheel

• High = .25/.30 cal (or high power .22cal)
• Med = .177/.22 cal
• Low = Sub 12 FPE 

Step 2 - Adjust regulator to appropriate setting per caliber.

• .177cal = 100 Bar
• .22cal = 100 Bar for <18gr ammo, 110 Bar for 18gr ammo, 130 Bar for >18gr ammo
• .25cal = 120 Bar for 25gr pellets, 140 Bar for all other ammo
• .30cal = 140 Bar 

Step 3 - Adjuster Hammer spring pre-load

• Hammer wheel MAX or 23/24
• Adjust pre-tension while shooting over a chronograph until desired speed is achieved
• If velocity stops increasing, that is max velocity for that regulator pressure

Recommended ammo weight per caliber:

• .177cal = 10.34gr pellets
• .22cal = 500mm and 600mm barrels, stick to 14gr up to 21gr. 700mm barrels can go up to 25gr.
• .25cal = 25gr up to 34gr
• .30cal = 44gr up to 50gr

These steps should create a <15 fps extreme spread and <5 fps standard deviation. 

Desired velocity range for pellets is between 860 to 910 fps

Desired velocity range for slugs is between 950 to 980 fps

The Crown is best suited shooting pellets, but it can handle light slugs if the settings are turned up. 

As long as you stop increasing the hammer spring pre-load once you reach your desired velocity, and you have your transfer port wheel on the correct setting, you will not be wasting air.