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 if the grenade is bounced properly into position, 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). This function is also helpful if the player wishes to fire at targets that are farther away than the detonation timer would normally allow. 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

 * When fired normally (Without holding the trigger) the Grenade Round makes a quiet whistling in flight. When the trigger is held, however, the round will make a noise remarkable similar to a tea kettle whistling, possibly as a gameplay strategy to alert attentive players to its presence.
 * 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/she died and someone else picked up the weapon, the player holding the M319 would take control of the dormant grenade.
 * 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's operator does not extract any empty shell casing. This could mean that it uses a caseless grenade round.
 * In the alpha build, the M319 has a red light on its side. This was removed later in the beta build.
 * The counter on the left of the weapon switches from "ARMED" to (very briefly) "LNKNG" just after launch, and then to either "IN AIR" or "LNKED" after the round is launched, depending on the firing mode; and finally to "BOOM!" upon detonation.
 * In first person a player can only look a total of about 70 degrees (+35 to -35) on the Grenade Launcher's reticule; clearly this being another 7 reference.
 * When you shoot a grenade that will deliver a fatal blow, a skull and crossbones will appear on the counter.

List of appearances

 * Halo: Reach