Rifle

In the actual sense of the word, a "rifle" is a weapon with a spiral grooved barrel that imparts a spin on a projectile to obtain better levels of accuracy than a smoothbore weapon, such as a musket or a shotgun. In the Halo universe sense of the word, a rifle can have several different meanings.

Summary
When regarding human weapons, there are a few forms of the word "rifle" used. An "assault rifle" is a firearm that may or may not be fully-automatic (and may posses a fire selector), that fires a round between a pistol or battle rifle. A "battle rifle" fires a large full-size rifle round and is usually, but not always, semi-automatic and often has a long full-size barrel. A "sniper rifle" can fire various high-caliber ammunition variants, and are almost exclusively semi-automatic. Their goal is to achieve high levels of accuracy and lethality, and have longer ranges than assault or battle rifles.

Regarding Covenant weapons, a "rifle" is used not to describe the technical nature of the weapon itself, but in the role it plays on the battlefield. For example, the plasma pistol and plasma rifle, while similar, are used for two different purposes. A rifle is larger than a pistol, often requiring both hands to use, but is smaller than a heavy weapon, such as the Brute shot or fuel rod cannon. This applies to both the plasma rifle and the beam rifle. The Covenant carbine is also considered a rifle and the spiker can fit into this list as well.

There are currently 30 known rifle variants in the Halo universe.

Assault rifles
Assault rifles are military service weapons that that fires intermediate rifle cartridge; merging the light machine gun's firepower with the submachine gun's compact design.

MA Series

 * MA1 Individual Combat Weapon System - The original MA rifle, precursor to all current MA variants.
 * MA2B Individual Combat Weapon System - Successor to the MA1. Functionally similar to the the MA5B. Occasionally used by Special Forces operators.
 * MA3A Individual Combat Weapon System - The precursor to the MA5B assault rifle. Retired from service, remains popular on the black market and among insurrectionist groups.

MA5 series

 * MA37 Individual Combat Weapon System - Introduced in 2437, known as the MA5 to the UNSC Navy and Marine Corps. In service with the UNSC Army up until the Fall of Reach. Featured in Halo: Reach.
 * MA5B Individual Combat Weapon System - Standard issue assault rifle in service with the Navy and Marine Corps up until late 2552. Featured in Halo: Combat Evolved.
 * MA5C Individual Combat Weapon System - MA5B replacement, with lower magazine capacity and higher accuracy. Featured in Halo 3.
 * MA5D Individual Combat Weapon System - Post-war successor to the MA5C, newest addition to the MA5 series. Featured in Halo 4.
 * MA5K Carbine - Uncommon carbine variant, wielded by Special Forces units such as the SPARTAN-IIIs.

Battle rifles
Battle rifles are military service weapons that fires a full-power rifle cartridge; providing greater effective range, penetration, and stopping power than assault rifles.
 * XBR55 Battle Rifle - Halo: Contact Harvest-prototype battle rifle.
 * BR55 Battle Rifle - Two-handed firearm firing in 3-round bursts. Featured in Halo 2.
 * BR55HB SR Battle Rifle - An updated version of the BR55. Featured in Halo 3.
 * BR85HB SR Battle Rifle - Post-war successor to the BR55 series. Featured in Halo 4.

Marksman rifles
Marksman rifles are military service weapons that fires a anti-personnel/magnum-caliber rifle cartridge; used to fill the "marksmanship gap" between the battle rifle and the sniper rifle.
 * M392 Designated Marksman Rifle - Accurate single-shot, medium-range rifle. Better known as the DMR. Featured in Halo: Reach.
 * M395 Designated Marksman Rifle - Post-war successor to the M392 DMR. Featured in Halo 4.

Nonlinear rifles

 * M6 Grindell/Galilean Nonlinear Rifle - Shoulder-carried, anti-vehicular, directed laser weapon. Featured in Halo 3, Halo Wars, Halo 3: ODST and Halo Reach. Better known as the Spartan laser.

Recoilless rifles

 * ARC-920 - Compact-channel linear accelerator carbine, fires high-explosive rounds at extreme velocities. Better known as the railgun. Featured in Halo 4.

Sniper rifles
Sniper rifles are military service weapons that fires anti-material/anti-vehicular rifle cartridge; used when accurate, long-range, and lethal force is needed.
 * Sniper Rifle System 99 Anti-Matériel - Long-range, two-handed sniper rifle, fire various 14.5x114mm ammunition variants. Featured in Halo: Reach.
 * Sniper Rifle System 99C-S2 Anti-Matériel - Variant of the original SRS-99. Featured in Halo 2.
 * Sniper Rifle System 99C-S2 Anti-Matériel B - Variant seen in Halo: Ghosts of Onyx.
 * Sniper Rifle System 99D-S2 Anti-Matériel - Variant of the SRS99C-S2 AM. Featured in Halo 3.
 * Sniper Rifle System 99-S5 Anti-Matériel - Post-war successor to S2 variants. Featured in Halo 4.
 * M99 Special Application Scoped Rifle - Man-portable miniaturized Magnetic Accelerator Cannon. Used by Avery Johnson in Operation: KALEIDOSCOPE.

Projectile

 * Type-33 Carbine - One-handed sidearm, fires homing crystalline ammunition. Better known as the needler.
 * Type-31 Rifle - Medium-range cousin of the needler. Analogous to the DMR. Better known as the needler rifle. Featured in Halo: Reach.
 * Type-25 Carbine - One-handed spike rifle. Analogous to the SMG. Better known as the Brute spiker.
 * Type-51 Carbine - Scaled-down, anti-infantry version of the fuel rod cannon. Analogous to the battle rifle. Better known as the Covenant carbine.

Particle

 * Type-50 Sniper Rifle System - Long-range two-handed weapon, primarily used by Kig-yar Snipers. Analogous to the SRS-99 sniper rifles. Better known as the beam rifle. Featured in Halo 2, Halo 3, and Halo 3: ODST.

Plasma

 * Type-25 Directed Energy Rifle - One-handed plasma-operated weapon typically wielded by Sangheili. Better known as the plasma rifle.
 * Type-25 Directed Energy Rifle/Jiralhanae variant - Variant of the standard plasma rifle wielded exclusively by Jiralhanae, with superior rate of fire. Featured in Halo 2 and Halo 3: ODST.
 * Type-51 Directed Energy Rifle/Improved - Two-handed plasma-operated weapon used mostly by Sangheili. Analogous to the MA5 series assault rifles. Better known as the plasma repeater. Featured in Halo: Reach.
 * Type-52 Special Applications Rifle - Sniper weapon, fires continuous beam of magnetically contained plasma. Better known as the focus rifle. Featured in Halo: Reach.

Deleted material

 * Gravity Rifle - A Covenant long-range rifle cut from Halo: Combat Evolved.