Nail Gun

The nail gun is the first weapon used by Kohta Hirano during the initial outbreak at Fujimi Academy. It is gas-powered and able to launch nails at a speed high enough to pierce a skull at moderately close range. Kohta creates a makeshift stock and sight for the nail gun to make it more like a rifle.

Overview
"The tip needs to be pressed down to set the safety off, which can make it a pain to use, but well, Kohta-chan took care of things." -Daisuke Sato

Plot
The nail gun was used during the initial Outbreak by Kohta, who added a makeshift stock as well as adding crude but usable sights for accurate firing and firing stability. It was used up until they reach Rika's house, where it is presumably discarded for other firearms (In the anime, he ran out of nails and used the Smith & Wesson given by takashi). Kohta was able to use it like a real firearm, displaying excellent marksmanship he had learned prior to the Outbreak. He even mentioned a Lethal Weapon 2 reference, in which one of the protagonists uses a nail gun to eliminate two of the hitmen.