The Shotgun is the third weapon in the game that comes with 35 ammo, 2 upgrades come with it: damage increasament and firing rate.

The Shotgun delivers medium damage, had a low firing rate, which can be increased with the upgrade, and comes with 35 ammo.

It's recommended to buy it once you enter the game as it's one of the best weapons to have early on. Rate of fire should be bought once you aquired the Rifle.