I just bought an HB22 Benjamin .22 calibre air pistol. When I fire the pistol, the bolt blows open. I pump up the pistol, three to eight times, open the breech, put in a pellet, close the breech, turn the breech bolt clockwise to lock the breech. Then I fire the pistol and the pellet goes out to the target, but the bolt blows back open. I can feel air coming back from the breech. I tested the velocity of the pellets with my Chrony and with eight pumps, a 14 grain pellet goes 450fps. Is this blowing open a normal part of the HB22 operation?