The Long Barrel increases the range of a weapon by 16%. Therefore, the longer the initial range of a gun is, the longer the maximum range will be. The attachment is available for submachine guns, shotguns and handguns. It is incompatible with the suppressor attachment, for balancing reasons. This is most effective on shotguns, as it increases the maximum range the pellets can hit a target before vanishing. On handguns, it's not as effective, except for the Executioner, where it makes the weapon much more effective. It also adds a physically longer barrel to the weapon as well.
The long barrel changes every weapon category differently:
100% longer range for all assault rifles except KN-44 and KVK 99m.
KN-44's range is increased by 13% and KVK 99m's range is increased by 30%.
Submachine guns have their minimum damage range increased by 25%.
Shotguns have their minimum damage range increased by 13% and minimum base damage decreased by 20% (meaning it does not help with one-shot kills, but allows them to reach further with decreased damage).
Handguns have their range increased by 13%.
Aesthetically, it adds an extension to a weapon's muzzle. It is now compatible with the Suppressor barrel attachment.
Some weapons allow players to attach the optional Long Barrel II after the normal Long Barrel is equipped. The weapon's range is greatly increased when equipping two Long Barrels.
Call of Duty: Mobile
In addition to the multiple barrel customizations, the attachment appears in Call of Duty: Mobile as the Extended Barrel, also referred to as RTC Tac Impaler in the attachment unlock screen. It is available to the BY15 and KRM 262 shotguns.
Call of Duty: Black Ops Cold War
"Extended shotgun barrel with chrome lined bore. Improves damage range."
Within Call of Duty: Black Ops Cold War, the Long Barrel returns as the Extended barrel family of barrel attachments, giving increased muzzle velocity for most weaponry it can be attached to. However, it gives increased effective range for Shotguns.