Heavy Caliber

Heavy Caliber increases damage of Primary Weapons (excluding Shotguns) at the cost of reduced accuracy by 15% and -5% per rank, at a maximum of 165% and -55% at rank 10, respectively.

Trivia

 * When it was first released, Heavy Caliber's original penalty was an increase in recoil as well as damage. However the recoil penalty did not affect recoil-less weapons (Flux Rifle, Ignis, Synapse, Paris, Lanka, and among others), effectively acting as another instance of Serration. This was confirmed to be unintentional in Warframe Prime Time - Episode 2 (9:40). The mod's penalty was changed in.
 * Currently, weapons that are not affected or barely affected by the accuracy penalty are shown below.
 * Amprex
 * Flux Rifle
 * Glaxion
 * Ignis (Helps somewhat due to a wider attack radius)
 * Opticor
 * Penta
 * Quanta (Vandal) (For regular attacks - cubes will be affected far more noticeably)
 * Simulor (Synoid)
 * Zarr