Flamethrower
Magazine Size: 100
Dual-Wieldable: No
The two-handed M7057 Flamethrower truly is a beast of a weapon. Not only does it rapidly raze your targets to the ground, it can be used to destroy a large ground of attackers.
Pros: Torching enemies with this huge gun is an easy way to clear out an area. You don't even have to be accurate with the Flamethrower to kill your target(s).
Cons: Like the Chaingun, the Missile Pod, and other heavy guns in Halo 3, the Flamethrower makes you walk super slow when holding it. It is also quite difficult to master and is only good for few situations during multiplayer.
Frag Grenades
Magazine Size: N/A - (You can hold 2 of each type of grenade at once)
Dual-Wieldable: No
This is your standard, no frills, hand grenade, but it does the job and it essential in maximizing your killing efforts. Its fuse is faster than previously seen in Halo 2, but the explosion from the Fragmentation Grenade in Halo 3 inflicts slightly less damage. You can only carry two at a time, but they're found everywhere on the battlefield.
Pros: Use of Frag Grenades is a crucial part of Halo's fundamental gameplay--they mustn't be ignored. They are a good way to finish what your bullets/projectiles have left still breathing on the battlefield.
Cons: You need to be accurate when lobbing these in the direction of a target.
Machine Gun Turret
Magazine Size: Infinite While Mounted to Tripod / 200 While Not Mounted
Dual-Wieldable: No
The most common turret weapon fires a blistering volley of high-impact slugs. The damage is devastating, but ammo and accuracy are limited. Like all turret weapons, you'll move slowly and lose many abilities while carrying the turret. As strong as Spartans are, you won't be able to pitch grenades or use any deployables once you tear this monster from its tripod base. Best case scenario: you're out of sight until the moment when you point the turret at an enemy and end their life.
Pros: The gun is also extremely effective when taking down a huge cluster of enemies--just start firing and tear them to shreds.
Cons: Remember that anyone manning a stationary turret is a sitting duck, making them an easy target for someone to frag.
Magnum
Magazine Size: 12
Dual-Wieldable: Yes
While the Magum is somewhat hard to come by during Halo 3's campaign mode, it is well worth swapping out at least one of your weapons for this powerful UNSC handgun. While each clip only has 12 bullets in it, they are enough to defeat 12 enemies if you nail them in the head. The Magnum, which is similar to the Magnum in the original Halo in feel, is as reliable as handguns get and is a crushing force that you should take advantage of. This recoil-operated sidearm is a perfect choice in close battles, and the fact that it is dual-wieldable makes it even more indispensable in your quest to shed enemy blood.
Pros: In addition to being a devastating firearm, the Magnum is also good at picking off shielded enemies. Aim for enemies' heads and make them eat lead.
Cons: Its range is low and you won't come across the Magnum very often in the game. It doesn't hold very many bullets, so you need to blast enemies with it that are close to you. Another drawback of the Magnum is that there is no zoom functionality on it, so call on its power when you are close enough to smell an enemy's aftershave, a scent that will quickly turn into the stench of you enemy involuntarily defecating in their undies once you point this silver firearm in their face.