I copied this from the manual...
Your shotgun is supplied with a plug to limit the capacity of cartridges in the magazine tube. Your country's regulations may not require this plug to be used so it may be removed.
When the barrel has been removed from the shotgun, insert a large bladed screwdriver into
the hole in the magazine spring retainer.(Fig 25)
While pushing down on the spring retainer with the screwdriver, and rotating in a clockwise direction approx imately 1/4 turn, the retainer will move to a position where the cutout in the retainer will align with a detent in the magazine tube, enabling the retainer to come out of the magazine tube. Be very careful at this point, as the retainer is holding a spring inside of the magazine tube and the spring is under tension.
Slowly pull back on the screwdriver to allow the magazine spring to push the retainer and capacity plug out of the magazine tube. (Fig 26)
You can download a copy from CZ here...
http://cz-usa.com/hammer/wp-content/uploads/2014/05/CZ-USA-Pump-Shotguns.pdf
