The M72 rifle is of German design. It uses an electromagnetic field to propel rounds at tremendous speed... and pierce almost any obstacle. Its range, accuracy and stopping power is almost unparalleled.
The Gauss rifle, also called a "coil gun," is a device used to propel a ferromagnetic projectile by accelerating it through a process of magnet induction. The Gauss rifle (and Gauss gun) are named after German mathematician Carl Friedrich Gauss, who formulated mathematical descriptions of the magnetic effect demonstrated by magnetic accelerators.
The most expensive small gun in 23rd-century post-apocalyptic Northern California, the M72 rifle is very powerful and accurate. It boasts the longest range in the game (together with its pistol counterpart and the sniper rifle) and a very high, 20-round magazine capacity. Its massive damage per round and the armor-piercing properties of the 2mm EC ammunition make it one of the most armor-negating weapons in the game.
This rifle averages 56, 41.25, and 23.15 Hit Points against unarmored, medium-armored, and maximally armored foes, respectively. It is particularly devastating with critical hits because the good armor penetration of its ammunition, when coupled with the armor-piercing critical hit effect, is enough to completely nullify the Damage Resistance of any target.
For a character with an average Critical Chance (5%), eye shots from the Gauss rifle do more average damage against heavy armor than what point-blank bursts from most machineguns do, at the same action point cost.
Though the M72 Gauss rifle has no shortcomings from a strictly combat perspective, the rarity of the 2mm EC can be a major problem. It often necessitates that secondary weaponry using more plentiful ammo types be utilized against lesser threats, in order to reserve the Gauss ammunition for the most dangerous engagements.
The Oil Rig has a few in some of the ammunition crates.
Some guards in the Shi temple have them. They can only be obtained by killing them, meaning one has to risk making the Shi hostile.
Can be found on Dumont and Deputy Karl in NCR. Both have to be looted for it.
When playing an evil character, Bounty hunters at high levels often carry Gauss rifles.
Lastly, coming across a random encounter with a cave that has something in them, the cave may be full of very well armed robbers. with a level around 19, the robbers will be equipped with combat armor, and some will be armed with this rifle (less in number compared to other weapons).
The S.T.A.L.K.E.R. series pays homage to the Fallout series with several weapons, while most of them were cut from the finished product the Gauss Gun was included in the main game and its sequel. It bears striking similarities to the M72 Gauss rifle including a very resembling external appearance, extraordinarily high accuracy and damage output as well as the utilization of rare 2mm projectiles as ammunition.