Much like the Logbook and Helmet the Weapon is a meta item. It cannot be used to build with. Attempting to use it in advanced build mode makes the game generate a small error message. However selecting it on your action bar while in Astronaut mode makes the Dave model aim the weapon. It can be fired by left clicking when it is selected. In its current form the weapon cannot be altered to fire differently and does 3 damage per shot to shielding and 5 per shot to blocks. Firing it at another player or NPC will make them them lose health. NPCs will return fire for a short time. If dropped the weapon shows up in space near you as an item and can be picked back up. This item cannot be sold to a shop. This item's appearance can be changed by editing the skin file. However, doing so will make all weapons you see appear the same as yours.
See weapon in use
To see the animation of aiming the weapon you can zoom out your camera by holding shift and using your pointing device's scroll down function. On a standard computer mouse you would roll the scroll wheel downward but on laptop track pads and other pointing devices it varies. When you use the item with the view zoomed out you can watch a stream of small cannon bolts fire from the weapon.
Replace lost weapon
To replace a lost weapon: