I do not have a P22, but thought that this information I found on rimfirecentral.com could help out some owners.
Original post on rimfirecentral.com http://www.rimfirecentral.com/forums/showthread.php?t=40667
Did you know that if you use the key operated safety/lock on the side of the P22 and then click the hammer of the gun to half cock the gun locks itself and becomes a paperweight? I know now. With the gun in half cock the lock can not be turned back to the "fire" position and the hammer can't be dropped to free it. I call this the "Catch P22". The gun can not be dissassembled either. Thats some safety that makes the gun never fire again. Take my word for it and do not try and and duplicate my dillema.
Once the hammer is cocked, simply slide your finger in BEHIND the trigger, and apply forward force while you turn the key to unlock the gun. Too simple. Tried it several times, with varying pressures, but it doesn't take much, just gotta releive the pressure that the hammer is putting on it.