M319 grenade launcher

The M319 Individual Grenade Launcher, more formally known as the Individual Grenade Launcher, Caliber 40mm, M319, is a single-shot, break-action explosives launcher used by the United Nations Space Command, specifically the UNSC Army. Due to its simplicity, ruggedness, and firepower, it has been a mainstay weapon in the UNSC Army since its adoption in 2263, and has seen action in several armed conflicts during nearly three centuries of use, with the Human-Covenant War as the most prominent. It saw use during the Fall of Reach.

Design Details
The grenade launcher has two firing modes. The first launches a single grenade at around normal grenade speed: after hitting a surface, the grenade detonates on impact with an opponent or after the time of a frag grenade's detonation, in which case the grenade will explode after bouncing off the ground once. The second firing mode shoots a grenade that explodes when the player wishes. This is performed by holding down the trigger, which fires the grenade but merely primes it; it will only explode after the trigger is released. This enables the player to lay a trap and essentially creates an explosive with a dead-man's trigger (a trigger that will go off once it is released, e.g. when the player dies). Like the fragmentation grenade in Halo: Reach, a player will take damage if hit by the grenade when it is merely primed.

Also, the grenade emits a form of EMP, similar to that of the plasma pistol, that can temporarily disable vehicles and energy shields, but only when used in the manual detonation mode.

The weapon utilizes a break-action breech loading system: after firing one round, the weapon must be reloaded, like many twentieth century shotguns.

Trivia

 * The grenade launcher has multiple nicknames among the fan community and Bungie alike, including "pro-pipe", a reference to the numerous grenade launchers in first-person shooter games, which have been collectively dubbed "noob-tubes".
 * The M319 IGL, having been manufactured in 2263, is the oldest known active service weapon utilized by the UNSC.
 * In the Beta, if a player fired the M319 and held the trigger until he or she died and someone else picked up the weapon, the player holding the M319 would take control of the dormant grenade and it would detonate, damaging or even killing anyone within range.
 * The M319 bears a very close resemblance to the real-life Russian GM-94. However, their similarities are merely aesthetic, as the GM-94 is a magazine-fed pump-action grenade-launcher using 43mm grenades. The M139 also bears a close resemblance to the American Springfield Armory M79 grenade launcher in both aesthetic and functional fronts. The two are break-action launchers that fire 40mm shells.
 * When reloaded, the M319 doesn't seem to need an empty shell casing to be extracted in some way. This could mean it uses some type of caseless grenade round or possibly a self-propelled grenade.