Call of Duty Modern Warfare's multiplayer scene is a constantly-evolving community in which players are free to customize loadouts, unlock weapons, and grind their favorite guns for new attachments and skins. The weapon progression is deep and satisfying, with visible progress happening nearly every match, just as long-term goals require lengthy time investment. The single-player experience is nothing to sneeze at either, with a solid, if short, character-driven story.
Several updates have attempted to balance out the meta of which guns are the most powerful in Modern Warfare's multiplayer, and more weapons will be added in the future. However, for now, the many available guns have settled into comfortable niches. There are some that are extremely strong no matter what, others that need specific attachments to be useful, and still more that may not be particularly strong but stand out as particularly fun. The rankings that follow are an attempt to group all the available weapons together into tiers that reflect their power, situational usefulness, and the fun they offer to the user.
D-Tier
Some weapons are just plain bad. These guns are neither strong nor fun to use; they can be safely avoided without risk of missing out on anything special. In the future as new weapons are added to Modern Warfare, these guns will likely never see the light of day unless they are buffed.
The Uzi is one of the most popular SMGs in the world for a reason, but these reasons are not reflected in Modern Warfare. Its slow rate of fire should make recoil very controllable, but in CoD the gun has a slow rate of fire and recoil that makes it hard to control. The effort of learning to control the gun is not rewarded with decent damage.
The SA87 LMG just doesn't cut the mustard when compared to other LMGs available. Marksman rifles in general are outclassed by both snipers and assault rifles, but the EBR 14 is the worst marksman rifle. Likewise, the Dragunov, the M19 and the Strela-P are all the worst weapons in their individual classes.
C-Tier
The FAL. A single-fire only gun in the assault rifle class. It has decent damage, but is essentially a marksman rifle with less range.
The AUG and PP19 are decent SMGs, but they can't compete with the better SMGs that are out there. MK2 and KAR98K are almost indistinguishable in their effectiveness, which isn't very impressive. Players should pick up an AR or sniper rifle instead. The X16 is the first pistol in the game, with respectable damage and an OK fun-factor, and as launchers go, the PILA is an effective choice with some superior options.
B-Tier
The FR 5.56, otherwise known as the FAMAS, is extremely fun to use. However, its 3-shot bursts make it unable to compete with other assault rifles. In Modern Warfare's hardcore mode, its a great option that will kill any enemy in a single burst, but in regular game modes it is just too slow.
The FN SCAR 17 does okay damage, but is really nothing more than a slightly inferior AK-47, while the M13 is just an all-around pretty good weapon. The 1911 much the same for a sidearm, but is about as plain as it gets.
The Model 680 and Origin 12 are both pretty lackluster shotguns with an abysmal accuracy. However, they both have a satisfying feel and will do the job at very short ranges.
The .357 revolver is one of the worst sidearms available, but with enough modifications can get shotgun rounds and become extremely fun and useful.
The JOKR launcher is useful because of its arcing shots, while the RPG-7 is useful against players at the cost of vehicle damage. They both have their merits, but are situational weapons.
A-Tier
The Oden is an assault rifle with high damage and low rate of fire, making it a strong choice with a unique feel. Meanwhile, the Kilo 141 offers high damage and a good fun-factor as the first AR in the game. The P90 is a good SMG with a high fire rate and large magazine. Its only downside is a low effective range.
The R9-O shotgun is surprisingly effective. Its two rapid shots per pump can be a little janky at first, but offer a lot of enjoyment and a unique feel. The M91 is a really good gun, but just not as good as the PKM, while the MG34 isn't a great competitor but offers fun gameplay. The HDR is a good sniper rifle, but not the best. The riot shield is S-Tier strong, but is one of the most toxic weapons in Modern Warfare, not to mention how boring it is to use.
On the exact opposite end of the spectrum, the combat knife is pretty terrible, but very fun to use when players try to make Modern Warfare challenges for themselves.
S-Tier
S-Tier assault rifles include the AK-47 with high damage and satisfying feel, as well as the M4A1: simply put, the best weapon in Modern Warfare. However, some of its luster is lost because everyone uses it. The PKM is the first and best LMG in the game. The AX-50 is the best sniper rifle, and using anything else is a disadvantage. Likewise, the .50 GS, better known as the Desert Eagle doesn't have much competition in the other sidearms.
The MP5 and MP7 trade blows as two of the most satisfying and versatile weapons in the game. They're both great, but the MP7 is the last SMG unlocked. They may only find competition from other SMGs with the addition of the Vector.
Meanwhile, the 725 is so good that it's broken. It's a fun double-barrel shotgun with crazy range, and multiple nerfs have done almost nothing to slow it down. Whenever the weapon is balanced, it may stay on the top of the list, but hopefully under more reasonable circumstances.
More content is constantly being added to CoD, so the best guns are liable to change. However, almost every weapon can find some way to be useful, or at least provide some entertainment in Gunfight.