A Magnum is a high caliber handgun that fires very powerful rounds. These pistols have large frames to withstand the high pressures of their cartridges, and often have long barrels to maximize bullet velocity. These firearms use Magnum ammunition, and appear in both revolver (most common) and semi-automatic (somewhat rarer) forms.
The standard "power weapon" in almost all Resident Evil games, the Magnum deals devastating damage to enemies and also possesses superb penetrating abilities. These guns will instantly decapitate a normal zombie when shot in the head.
However, Magnums often have a small supply of ammunition available and a relatively low clip capacity. Thus, their use is limited and recommended only for boss encounters and hard-to-kill enemies. Plus, they have a slow rate of fire due to strong recoil, and thus are generally unsuited for crowd control.
The Magnum is the second most powerful weapon type in Resident Evil next to the Rocket Launcher.
In Resident Evil: The Mercenaries 3D and Resident Evil 6, the player can equip certain Skills that affect how effective Magnums are.
In Resident Evil: Revelations, enemies have a specific set of resistance and vulnerability to each weapon type. In Raid Mode, Raymond, Lansdale, Rachel, HUNK, and Lady HUNK have inherent skills that make them more effective with Magnums.
In Resident Evil 6, after completing all campaign chapters, a skill called "Infinite Magnum Ammo" will be available for purchase, granting unlimited ammunition to the weapon. The skill is one of the most expensive skills in the game.