Below I have described in detail all of the UNSC, covenant, and Promethean weapons, including when and how to use these weapons. For the covenant and Promethean weapons, I have also provided the best strategies to overcome enemies with these weapons. The x/y after each gun name refers to the ammo per magazine/maximum extra ammo. Notice that the strategies are intended for use against AI in Spartan Ops and Campaign. These strategies do not necessarily apply when playing against human players in War Games.
“Headshot weapons” are a group of weapons with unique properties. A single headshot to an unshielded enemy from a headshot weapon deals infinite damage, allowing you to easily kill any rank of enemy on any difficultly. Headshot weapons are the most accurate weapons in Halo 4 and they all have scopes. This allows you to pick off enemies from a distance, which is usually the safest tactic on higher difficulties. You can also use headshot weapons up close, including against shielded enemies. Remove the enemies shields (preferably with an overcharged plasma pistol), and you then can finish them with a single headshot from a headshot weapon.
Assault rifle – 32/128: The assault rifle is the most accurate fully automatic weapon in Halo 4. Not only is it accurate, it also has very low recoil, so you can fire an entire magazine at once and still retain accuracy. When you do not have stronger weapons (such as the incinerator cannon or SAW), you can use the assault rifle to kill Promethean knights. Whenever possible, use either grenades or an auto sentry in combination with your assault rifle to more easily kill knights.
Battle rifle – 36/108: The battle rifle is an accurate headshot weapon with a 2x scope. It fires a 3-shot-burst each time you pull the trigger. These 3 bullets travel in a tight spread, increasing the area that you hit and allowing you to get a headshot even if your aim is a bit off. Because it fires 3 shots, the battle rifle is one of the highest damaging headshot weapons, so it is one of the best weapons for fighting Promethean watchers. Because watchers do not have heads, you must kill them with repeated body shots, so the higher damage of the battle rifle allows you to kill them in fewer shots. The downside to the battle rifle is that it consumes ammo very quickly.
DMR – 14/42: The DMR is an incredibly accurate semi-automatic headshot weapon with a 3x scope. It has practically no recoil and is just as accurate as any of the sniper rifles. Therefore, the DMR is great for picking off enemies from a distance. Using the DMR, you can easily kill light infantry from so far away that they cannot return fire. There DMR is also very effective up close if you do not use the scope.
Magnum – 8/32: The magnum is a secondary headshot weapon with a 2x scope. While it fires only one shot per trigger pull, the magnum has an incredibly high fire rate. However, I suggest that you instead fire slowly and carefully to conserve ammo and more easily get headshots. The magnum is not as accurate as the other headshot weapons, so you will need to get closer to your target when using it.
Railgun – 1/5: The railgun is a charge up weapon similar to the UNSC Spartan laser. It deals less damage than the Spartan laser, but it takes less than half the time to charge up. The railgun does not produce a targeting laser (unlike the Spartan laser), so enemy AI do not know when you are charging up a shot. Though railgun rounds do not travel instantly, they travel very quickly and home slightly on infantry, so it is easy to use the railgun at close or medium range. A single shot from a railgun can remove the shields of any knight, allowing you to finish them with a headshot. This combination allows you to quickly kill knights from a distance and up close, so it is one of my favorite methods.
Rocket launcher – 2/8: The rocket launcher, as implied by its name, fires powerful, explosive rockets. These rockets travel relatively quickly and accurately, so you can successfully use the rocket launcher from a fair distance. It deals enough damage to kill a knight or an elite in a single shot, though you rarely have access to the it during the campaign. In general, you should fire the rocket launcher at the feet of your enemies so that they cannot side step it. The rocket launcher has a 2x scope and it can lock onto enemy aircraft.
SAW – 72/216: The SAW is a powerful light machinegun great for killing Promethean knights. It deals the highest damage per second of all of the fully automatic weapons due to its incredible fire rate. It also has a huge magazine, which more than compensates for the high fire rate. The saw is great for killing knights; you can easily kill any rank with less than a single magazine of SAW ammunition. The downside of the SAW is that is fairly inaccurate, so you need to get up close when using it.
Shotgun – 6/18: The shotgun deal a large 17 wsm ammo amount of damage at point blank range, but it loses damage the farther away you get. If you are more than 2 meters away from your target, the shotgun deals no damage at all. I do not suggest that you use the shotgun during the campaign because it requires you to charge enemies. On higher difficulties, charging puts you at great risk. Furthermore, at point blank range, the shotgun still does not deal enough damage to kill either an elite or a knight in a single shot. Therefore, it is much safer and more efficient to use other weapons.
Sniper rifle – 4/12: The sniper rifle is the most accurate UNSC weapon, and it allows you to pick off enemies from very far away with its variable 5 – 10x scope. Even on legendary, the sniper rifle is useful against elites because it can kill them in only 2 headshots. (Elite generals require 4 headshots to kill, so you should use other methods to kill them). Because of its pinpoint accuracy, you can kill elites from so far away that they cannot return fire. The sniper rifle is especially useful for sniping enemies out of turrets because they cannot move to avoid your shots. Whenever possible, I suggest that you snipe elites operating a wraith’s plasma turret so that you can more easily destroy or hijack the wraith.
Spartan laser – plasma/25% per shot: The Spartan laser is one of the highest damaging weapons in the game, but it is also one of the hardest weapons to use. In order to fire the Spartan laser, you must first charge it up by holding down the trigger. After you charge it up for roughly 2 seconds, it fires a powerful, accurate laser. You can use the Spartan laser from a distance because it has a 2x scope and the laser travels infinitely. However, as you charge up the Spartan laser, it creates a smaller targeting laser visible to all enemies. Therefore, infantry can easily avoid the laser, so it is only useful for destroying vehicles. During the campaign, you only have access to the Spartan laser when you also have access to powerful vehicles (such as a Scorpion or Mantis), so I suggest that you use the vehicles instead.
