Here are all of the “official” Halo 3 Weapons List & Descriptions we found at Halo3.com. However, they didn’t list everything. For example, we couldn’t find the Gravity Hammer listed anywhere at Halo3.com, but we know from experience that it’s definitely in the game.

Confirmed Halo 3 Weapon Descriptions:

M6G Pistol
The M6G Pistol is a typical UNSC sidearm. It fires high explosive bullets witha relatively fast rate of fire and good accuracy. While hardly a sniping weapon, in the hands of a trained marksman the M6G can remain very accurate at long distances.

M7 SMG
The SMG is a UNSC issued, gas operated projectile weapon capable of continuous fire. The impulse-to-mass ratio of this weapon necessitates that the user constantly readjust aim during sustained fire. The SMG’ s main advantage is its high rate of fire.

MA5C Assault Rifle
The MA5C is a fully automatic, air-cooled, gas-operated, short-to-mid range weapon. The weapon houses an onboard electronics suite, including a screen indicating rounds left in the magazine. The weapon’s power is described as falling somewhere between the MA5B Assault Rifle and the BR55 Battle Rifle.

M90 Shotgun
The M90 Shotgun is the resident UNSC close combat weapon. Because of its extreme stopping power, the M90 is often wielded in tight or confined conditions, where the close ranges are conductive to the shotgun’s mode of operation. It is, however, a very large and heavy weapon.

BR55 Battle Rifle
The BR55 Battle Rifle is a UNSC gas-operated projectile weapon. It fires a larger caliber bullet than an assault rifle, giving more power but also more recoil. The BR 55 is restricted to three-round bursts of fire. The rifle is an excellent all-around weapon. Its biggest problem lies in its magazine capacity - allowing only 12 shots before reloading.

SRS99D Sniper Rifle
The SRS99D Sniper Rifle is the primary long-range rifle used by UNSC forces. It is, alongside its Covenant counterpart the Particle Beam Rifle, the most accurate, and arguably the most powerful infantry-sized weapon in both arsenals. The rifle’s only drawbacks are its cumbersome reload and its bulky, thus necessarily scarce, ammunition under typical battlefield circumstances.

M41 Rocket Launcher
The M41 Rocket Launcher, alternatively called the “Spanker” or “Jackhammer,” is a heavy ordinance weapon of the UNSC arsenal. The M41 sports a 2x scope and can fire rockets over long distances with devastating accuracy.

M6 Spartan Laser
The M6 Spartan Laser is a shoulder-mounted direct energy weapon used by the UNSC. It fires an extremely powerful red laser, capable of destroying vehicles and infantry with one accurate strike. When the trigger is pulled, a targeting dot is projected. The laser will then charge for three seconds before firing its powerful and destructive burst.

Plasma Pistol
The Plasma Pistol, like the Plasma Rifle, fires directed energy bolts instead of traditional projectile ammunition. This Covenant weapon is capable of quickly firing low-powered shots, or of charging a single high-powered blast which can rapidly deplete energy shielding. This high powered shot makes the Plasma Pistol a formidable strategic weapon if used in concert wit other infantry weapons.

Plasma Rifle
A common light weapon used by Covenant forces, the Plasma Rifle uses plasma technology firing directed energy bolts instead of projectile ammunition. The plasma rifle is particularly effective against shielded bipedal opponents.

Needler
Razor sharp crystalline projectiles are fired from this elaborately designed Covenant weapon and it is widely believed that they use heat and organic signatures to home in on targets. Although easily deflected by energy shields, the needles cause a chemical reaction in close proximity resulting in an explosive effect.

Brute Shot
Firing explosive grenade-like projectiles, this Brute weapon is also furnished with a razor sharp, stock mounted bayonet used in close-quarters combat. With only six rounds per ammo belt, the Brute Shot is effective, but limited.

Carbine
An unusual Covenant projectile weapon, this powerful, accurate, and scoped weapon effectively shoots tiny fuel rods of fissile material. The shielded auto ejecting magazines each hold 18 rounds of radioactive ammunition.

Particle Beam Rifle
A hand carried particle beam acceleration weapon. Its range is basically only limited by its five or 10x zoom scope, and atmospheric conditions. The rifle carries a power cell good for up to 18 bursts and charges very rapidly for a weapon of this type.

Brute Spike Rifle
Holding 40 spikes per magazine, this vicious and dangerous rifle is favored by Brutes and in fact, is based on their native pre-Covenant technology. Old as its technology is, the rapid firing razor-sharp projectiles can tear through armor and flesh with ease.

Energy Sword
A combination of ceremonial elegance and practical power, the twin-bladed Energy Sword can be used as a slashing melee weapon, or in correct fighting technique, the wielder waits until the opponent reaches a perfect distance and lunges forward in a ferocious attack.

We’ve seen the videos online of a multiplayer game featuring a flamethrower and fire or incendiary grenades, but we haven’t found them yet.

*UPDATE* Flamethrower confirmed! It’s in the central, lower level of the multiplayer map Construct. Haven’t found a description for it yet, but we’ll add that as soon as we find it!

Also, there’s a Gravity Hammer in a couple levels too. No description, but it’s for real.

Or you can just fire up Forge and try, test and experiment with every new Halo3 weapon.