So the thing about the weapons in halo is that they are constantly changing from game to game. Sometimes the actual gun will be the same but it will have different damage or range capabilities.

SMALL ARMS

PISTOL - unique to halo 1 and halo reach special anniversary gametypes it is very powerfull with a fast rate of fire
MAGNUM - unique to halo 2 and halo 3, a slow shooting weak weapon with no scope
ODST PISTOL - This silenced pistol comes with a 2X zoom and a 12 round clip, makes for a great backup weapon.
PLASMA PISTOL - a covenant plasma weapon with a high rate of fire that takes down a shield fairly quickyly. if held can charge up to create a large ball of plasma that follows its target to completly drain shields or render a vehicle unable to move for a short period of time

AUTOMATIC

NEEDLER - Concentrated plasma round as sharp as a needle with explosive results.
SMG - Automatic with a 180 round clip; can be dual-wielded.
SPIKER - A covenent automatic weapon used by brutes; shoots hi-paced plasma based spike-rounds.
ASSAULT RIFLE - Automati, 60 round clip; this rifle is the Spartan standard issue.
PLASMA RIFLE - a covenant automatic weapon that shoots plasa bullets at a very fast pace but overheats quickly and drain shields very fast.
BRUTE RIFLE - equvalent to the plasma rifle with increased speed and overhead speed
PLASMA REPEATER - a covanent weapon equivalent to the plasma rifle exept that it is possible to reduce the overheat time by pressing the reload button.

PRECISION

ODST RIFLE - Silenced + automatic + scoped = rape.
DESIGNATED MARKSMAN RIFLE - AKA DMR - Reaches version of the br, this is a single shot rifle with a 12 shot clip.
SNIPER - A long ranged rifle with 5X and 10X zoom. Head shot is death, two body shots is death.
BATTLE RIFLE - AKA "BR" - Standard spartan rifle comes with a 36 shot clip which fires in bursts of 3. Also comes equiped with a 2x scope.
NEEDLE RIFLE - a covenant weapon equivalent in power to the dmr automatic or semi-automatic shoots slightly faster then the dmr slighty reducing accuracy.
FOCUS RIFLE - a covenant weapon that shoots a highly concentrated large beam of energy in a strait line for an infinate distance untill it hits a solid object with a 2x and 4x scope
CARBINE - a covenant semi-automatic high speed high accuracy weapon in every halo exept halo reach
BEAM RIFLE - a covenant equvalent to a sniper rifle with a 2x and 4x scope that shoots extreamly fast. (if shot too fast will overheat.)

HEAVY WEAPONS

CONCUSSION RIFLE - Shoots an overcharged plasma round for maximum damage; has a 6 round clip.
SPARTAN LASER - Four concentrated lasers combined to form an extremely powerful, accurate blast. Capable of taking down a vehicle with no problem.
ROCKET LAUNCHER - This double barrel rocket launcher will destroy anything in its path, no questions.
PLASMA TURRET - You can rip one of these babys off a gunship or off a turret stand. Extremely fast and powerful, the plasma turret will take things out quickly.
HUMAN TURRET - You can rip one of these babys off a gunship or off a turret stand. Extremely fast and powerful, the plasma turret will take things out quickly.
PLASMA LAUNCHER - If charged up can shoot 4 plasma grenades at a time, also has lock on capabilities.
BRUTE SHOT - Six round highly explosive rounds; also has a large curved blade; makes for an excellent close combat weapon.

CLOSE QUARTERS

ENERGY SWORD - split bladed plasma-based sword when wielded the energy sword takes is shape; when not wielded, reduced to just the handle.
MAULER - A covenent close quarters dual wieldable shotgun-type weapon. Nuff' said.
SHOTGUN - Pretty much the same as any shotgun.
GRAVITY HAMMER - One swing will destroy just about anything!