This papercraft is a M9 High-Explosive Dual-Purpose Grenade (aka Fragmentation grenade, shortened Frag grenade, or simply Frag,), a UNSC-issued grenade that functions in a manner very similar to contemporary hand grenades in the science fiction video game Halo series, the paper model was created by PepMaster.
HE-DP stands for High-Explosive Dual-Purpose. This designation means that it is designed to be effective against infantry and lightly armored vehicles. AP FRAG can be viewed on the Halo: Combat Evolved M9's olive casing. AP designates "anti-personnel", indicating the weapon's intended use.
The grenade has a hard metal casing, with a frangible design meant to break apart into small, regular shards. This surface creates consistent, reliable fragmentation patterns for the grenade, rather than randomly rupturing along metallurgical faults. The grid-shaped casing houses a charge of high-explosive fitted with a mechanical primer. When the charge detonates, it shatters the grenade's casing, sending shrapnel flying away at high velocity.
In all Halo games, the grenade must first hit the ground before exploding. In Halo: Combat Evolved, the grenade would not detonate mid-air. In Halo 2 and Halo 3, it would bounce and explode mid-air a moment after bouncing. But in Halo 3, if the grenade was thrown up, and hit a surface going up, it would not explode until it hit the ground. This presumed to be a safety feature, ensuring the grenade would only explode after striking a surface after being thrown, and not in the user's hand. This may explain the lack of a "spoon", or handle, on the Halo 2 and 3 M9 HE-DP grenades. The spoon is a device that is gripped while the grenade is being primed. It ensures the grenade will not explode until after the spoon is released, as it starts the fuse of a grenade as it flies through the air after it is thrown. In Halo: Combat Evolved, the spoon would have negated the need for this Halo 2 safety feature.
The grenade is primed with a small button located on the "handle", quite unlike modern fragmentation grenades which use a pin that must be pulled before priming.
In Halo: Combat Evolved, the fragmentation grenade left a white smoke trail behind it when thrown and would create sparks when it landed after being hurled, indicating that the grenades fuse could be a gas-release system. The grenade would be primed with pressing a button, release gas when in mid-air and then detonate when landing in a static position. This would make the grenade's detonation system depend on placement rather than timed detonation.
In Halo: Combat Evolved and Halo 2, four of these grenades may be carried at a time. This was reduced to two in Halo 3 due to the presence of four grenade types, but increased to three in Halo 3: ODST and in Halo: Reach the player is again able to carry four grenades, but only if the settings are changed to carry this amount. [Source: wikia]
You can download the papercraft model template here: Halo: Reach - M9 High-Explosive Dual-Purpose Grenade Free Paper Model Download