Dual Mags decrease the time needed for every odd reload (e.g. first, third, fifth, and so on) by using two magazines taped together. The following reload will be the normal reload and take the normal amount of time. The odd reload depicts the player removing the spent magazine, flipping it around, and inserting the second, fresh magazine. It is available for all assault rifles (except the M14 and the G11), as well as the AK74u, the MPL, and the RPK.
With the exception of the RPK, the attachment also gives the player two extra starting magazines when the player spawns. For example, the FAMAS, with a magazine size of 30, starts with 90 reserve rounds normally, but with Dual Mags, it starts with 150 reserve rounds.
Since it speeds up reload times and provides more ammo, it reduces the need for Sleight of Hand and Scavenger, but using either or both perks can increase the immediate usefulness of this attachment. However, it should be noted that Dual Mags used with Scavenger Pro do not grant any extra ammunition that is already provided by the perk. Overall, it is a strong attachment choice as it opens up tier 1 and 2 slots to other perks such as Flak Jacket and Hardened to maximize the potential of the player's loadout. For balance purposes, this attachment cannot be paired with Extended Mags or Rapid Fire via Warlord.
Dual Mags reappear in Call of Duty Online, available to assault rifles and submachine guns. In addition to decreasing the time needed for every odd reload, the attachment gives one extra magazine when spawning, and two extra mags to the maximum ammunition.
Dual Mags return in Call of Duty: Advanced Warfare, fully referred to as Dual Magazine. It is available to some assault rifles (AK12, ARX-160, HBRa3, MK14, STG44, M16) and submachine guns (KF5, ASM1, SN6, AMR9). As an addition, when reloading an empty magazine, the weapon isn't cocked if it's an odd reload. Furthermore, the Dual Magazine can now be paired with Extended Mags or Rapid Fire, unlike in Black Ops.
In campaign, dual magazines can be seen on some weapons on the ground such as the KF5 and the SN6, but they are unobtainable.
In Call of Duty: World at War, the Extended Mags attachment for the MP40 is titled "Dual Magazines" but it just adds the ability to use two magazines as one on the MP40, therefore doubling capacity.
Taped magazines appear on most Assault Rifles and SMGs in Black Ops II when using the Fast Mag attachment, however it is purely cosmetic and every reload is sped up whether or not a loaded magazine is taped to the empty one, unlike Dual Mags.