The weapon system in Modern Warfare II is a modified version of the weapons and Gunsmith system found in Modern Warfare, with a limit of five mod slots. Primary weapons are divided into seven types: submachine guns, assault rifles, shotguns, battle rifles (high damage, high recoil select-fire rifles with low capacity), marksman rifles (high damage, accurate, exclusively semi-auto/manually-operated rifles, with iron sights), light machine guns, and sniper rifles. Weapon inspection animations are more intricate than it was in Modern Warfare, with the user often checking the magazine and/or chamber in each of the inspect animations. The current ammunition type (hollow points, incendiary rounds and the like) can also be seen. As of Season 1, inspect animations now correctly account for if the weapon is empty or not; this was not the case during the multiplayer beta and launch builds of the game.
Many weapons are now classified under a “Weapon Platform” system, which groups multiple weapons (which may cover several different types) in the same real world weapon family into a single set, with individual weapons within the Weapon Platform being classified as “Receivers”. Weapons under a Weapon Platform share a progression system that lets the player unlock platform-specific shared attachments.
Because of this, a number of weapons can make identical clones, allowing you to run two of the same weapons in one loadout, with only very marginally different stats (a difference of a few percent). The AK-103 and RPK can both become an AKMN, and the AUG A3’s LMG and assault rifle variants can be changed around to be the Steyr AUG A3-CQC. Additionally, the SR9 and HK91, as well as the M4 and 16 can be turned into each other, and the SCAR-H can be turned into the Mk20 SSR, though these all have different fire modes or calibers in game, justifying different damage, range, and accuracy stats. Why something like an AKMN built from an RPK has slightly higher accuracy than one built from an AK-103 but slightly lower damage is entirely unexplained.
The current known Weapon Platforms with multiple receivers in Modern Warfare II are the following:
Through the use of grip attachments, the “Tactical Pistol Raise” benefit introduced in MWII is the ability to instantly draw the player’s sidearm without fully lowering their primary weapon. Dual-wielding makes a return in Modern Warfare II, although it is regulated to the grip attachment of the weapon instead of being a weapon perk and it’s only restricted to handguns exclusively.
Various executions (finishing moves) that use a firearm in this game now involve other weapon types, in addition to a pistol unlike in prior games. If the player has a weapon of the same class (assault rifle, SMG, etc) as a given execution’s default weapon, the player’s custom weapon will be featured instead.
Modern Warfare II introduces extensive and realistic water physics, a significant improvement over Black Ops: Cold War, the previous game in the series to feature water mechanics. Unlike in Cold War, primary weapons can’t be fired underwater and only handguns can, albeit with a reduced efficiency. Shooting into water and explosions cause ripples and mines float when thrown onto water. When swimming on the surface, water flows into the weapon’s details and the weapon along with its user can get wet.