The PX4 Storm is a semi-automatic handgun manufactured by Beretta of Italy. It is available chambered for 9 mm, .40 S&W or .45 ACP. Built of lightweight polymer components on a compact frame with a 4-inch barrel, the PX4 Storm is optimized for concealed carry by law enforcement and security personnel. A number of the PX4 components are interchangeable to maintain a low profile in clothing. The magazine release can be installed on the left or right side of the pistol, and the slide catch is replaceable with a more flush version to avoid snagging. The back strap -- the tail end portion of the handgrip -- comes in three interchangeable thicknesses to balance grip ergonomics with requirements for concealment.
Remove the magazine by pressing the magazine release button at the bottom of the trigger guard.
Lift the U-shaped back strap retaining spring in the lower part of the pistol with a screwdriver and grasp the spring with your fingers. Remove the back strap retaining spring from the grip.
Pull the back strap downward and off the grip.
Place the new back strap in position on the grip.
Push the new back strap in forcefully until it is installed in the seat of the grip.
Install the U-shaped back strap spring into the lower part of the grip. Insert the spring shafts into the rear seat of the holes at the back of the pistol grip with the bent part of the spring facing toward the muzzle.
Reinstall the magazine.