Heavy Caliber

 increases damage and reduces accuracy of Rifles. update 10.4 changed the negative effects from increasing recoil, to reducing accuracy. This actually has a serious negative effect on weapons that are not 100% accurate such as the Soma.

Bugs

 * When released, did not add recoil to recoil-less weapons (Flux Rifle, Ignis, Synapse, Paris, Lanka, among others), effectively acting as a pure damage boost. This was confirmed to be unintentional in Warframe Prime Time - Episode 2 (9:40). This was later "fixed" in update 10.4, reducing accuracy instead of recoil. This however hurt non-pinpoint accuracy rifles even more, making even accurate guns like the Soma spread bullets considerably at max rank.

Media