The large-framed, gas-operated N99 was selected as the standard issue conventional sidearm of the United Statesmilitary, following the phaseout of the N80 in 2051. The long-barreled pistol remained in service for 26 years, until the Great War destroyed the United States. The pistol is designed to withstand the most extreme conditions, which was one of the requirements for a new service sidearm. It can also be repaired easily by anyone with even the most basic technical knowledge. This includes both clearing misfeeds and restoring a unit to working condition after long exposure to elements without maintenance.
These features also make it popular with wastelanders, who appreciate the ease of maintenance. It remains a common weapon, as even though many civilian units were ruined, they can easily be restored by anyone with some repair knowledge. Even damaged units can be used reliably, though they will offer subpar performance and jam frequently. The number of manufactured pistols means that parts are easy to come by, however.
A more powerful alternative to the 9mm pistol, the N99 performs well against a variety of early and mid game targets, though its ammo is a bit more rare. It has slightly misaligned iron sights, with the front post being offset to the left ever so slightly. However, this is a non-issue on shorter ranges.
↑Fallout 4 loading screen hints: "Small, dependable, reasonably powerful and widely available, the 10mm Pistol has been a staple of Wasteland combat since the bombs first fell."
↑The Lone Wanderer: "Your gun is jammed? Can I take a look at it?" Pek: "Sure, I guess. Can you fix it?" The Lone Wanderer: "Sure can. Here, just pull this back to clear the chamber." Pek: "Wow... that's... that's easy. Now at least I can shoot back at those mutant bastards. Are you ready?" (Pek's dialogue)
↑ 4.04.1Citadel terminal entries: N99 10mm Pistol: "The 10mm N99 sidearm was standard issue military gear following the phase out of the N80 in 2051. The N99 was known for its ability to survive in the harshest of conditions and in many tests, the weapon was able to reliably be restored to working condition after an extended period of time exposed to hard elements and without maintenance. The N99 proved to stand up to its claims and as a result, is one of the most common weapons found in use in the Wasteland. While many civilian weapons were ruined beyond use in the exterior conditions following the war, the N99 is commonly able to be easily restored to working order by anyone with the most basic knowledge of firearm mechanics. However, an N99 in poor condition can often deliver low target and armor penetration, frequent jamming, and greatly reduced accuracy. Fortunately, the weapon was produced in great numbers and units are available for replacement parts."