Not a lot of pieces.
NOTE: you need 2 grey and one black, these are the long ones. The firing pin is black. Stronger.
I used a small part from KILLERK's gun, the rest is my idea, if your gun is similar, keep in mind I didn't get any ideas other than from KILLERK.
Step 1: Make the Handle.
Step 2: Make the Firing Pin.
You need to use black (stronger) unless you want it to shoot only 1 foot.
Put tape on the back to strengthen it.