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 produced by Misriah Armory and 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 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 proved very effective during the Insurrection; although it is less effective against energy shielded Covenant foes, it can be used to deadly effect against unshielded targets. Because of the weapon's reliability and power, it will likely continue to be fielded by the Army.

Design details
The M319 IGL fires high-explosive dual-purpose grenades. The grenade launcher has two firing modes. The first launches a single grenade: after hitting a surface, the grenade detonates on impact with an opponent or after about two seconds, in which case the grenade will explode after bouncing off the ground once. The second firing mode shoots a grenade that explodes when the user wishes. This is performed by holding down the trigger, which fires the grenade but merely primes it, leaving the detonation contents inert; the grenade will only explode after the trigger is released. This enables the user 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 user dies). This function is also helpful if the user wishes to fire at targets that are farther away than the detonation timer would normally allow. Players are advised to use manual detonation against enemies in multiplayer, as players move around much more than computer enemies and thus are harder to hit with a proper bounce. As well, if a manual detonated grenade is exploded close enough to an enemy, is will kill them instantly. This isn't an easy thing to do, but if done well will make the grenade launcher a very deadly weapon.

Also, the grenade emits an electromagnetic pulse upon detonation, 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, the grenade makes a quiet whistling while in flight. When the trigger is held, the round will make a noise similar to that of a much louder whistling, which can serve to alert attentive players to its presence.
 * The grenade launcher is commonly known as the "pro pipe", a reference to grenade launchers in other first-person shooters, primarily the Call of Duty series, which are collectively known as "noob tubes" due to their ease of use.
 * The M319 IGL, having been manufactured in 2263, is the oldest known weapon utilized by the UNSC.
 * In the Halo: Reach Multiplayer 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 that uses 43mm grenades. The M139 also bears a close resemblance to the American Springfield Armory M79 grenade launcher in both aesthetics and function. Both are break-action launchers that fire 40mm shells.
 * When reloaded, the M319's operator does not extract an empty shell casing. This could mean that it uses a caseless grenade round or the round utilizes rocket propulsion, which can be supported by the fact that there is a fire trail extending from the back of a grenade in flight.
 * In the alpha build, the M319 had a red light on its side. This was removed in the beta build.
 * The counter on the left of the weapon switches from briefly displaying "ARMED" to "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. This is also present in the M460 AGL.
 * When the grenade is fired from the weapon and set to manual detonation, a skull and crossbones symbol will appear below the distance counter indicating the number of targets in its explosive radius.
 * In campaign, kills with the grenade launcher always reward the player with the EMP Blast Medal despite some enemies, such as the Unggoy and Jiralhanae, do not possess energy shielding and therefore could not be affected by EMP blasts.

List of appearances

 * Halo: Reach