lasgun
We bring the light of the Immortal God Emperor to the furthest parts of the Galaxy
Lasgun or otherwise known as Lasrifle is one of the two inseparable items (with the other being the T-shirt ceramite vest) of the trillions of Imperial Guardsmen out there fighting for the Imperium Of Man. While the weapon lacks the stopping power comparing to the Bolter or T'au Railgun, its ease of production, the lack of ammunition requirement, and most important of all, the sheer amount of Imperial Guardsmen will more or less make up for the Lasgun shortcoming.
After all, nothing beats unleashing an ocean of metal-melting laser bolts in the face of your opponent.