Step 1: Hopper and Barrel
Step 3: Butts
You can choose between the 2 butts.
If you are building the pistol, then check the last picture for reference.
Step 6: Other bits
2) Rails (make the gun stronger)
3) Hopper cover (highly recommended)
Step 7: Monopod
You can design your own monopod base if you like, I prefer the simple option.
Step 8: Firing
2) Shut lid
3) Pull back the pin slide until the gun clicks
4) Pull the true trigger (or if you want push the block trigger)
If the shot fails (very rare), the gun is installed with an access hole so the bullet can be pushed back into the firing slot easily. The hole is located above the barrel.