This Mod, does not make your gun into a Periscope, but is for an off-brand gun, that I’ve had for quite a while.
The front extends out and can be used as a periscope, which can be shot where you look through the scope. Here are some pictures
Step1—Unscrew the blue casing, above the 2 barrels.
Step2—Pry off the black pumping mech.
Step3—Unscrew the rest of the gun.
As you can see the insides are very small.
Step4—Take out the internals. (Optional: take out all of the periscope parts) Cut off the Stub on the front
of the orange piece/barrel.
Step5—Glue a CPVC Coupler onto the orange piece.
Step6—Wrap some duct tape around the CPVC/Airtank
Step7—Cut out the case enough for the coupler to fit in.