For any non-integer magazine values the magazine size is simply rounded to the nearest whole number. For example, a Vectis Prime modded with a max rank Depleted Reload will have a calculated magazine size of 2 × (1 + -60%) = 0.8, which will simply round to 0.8.
The calculation for reload time using reload speed is: Base Reload Time ÷ (1 + Reload Speed Bonus)
This mod can be combined with Primed Fast Hands for a reload speed increase of 103%.
Trivia
When this mod was first introduced, equipping it on the Vectis would reduce the magazine size to zero, causing the Vectis to draw directly from its ammo reserves and allowing it to fire very quickly. This was fixed in Hotfix 17.0.3 (2015-08-04); now the Vectis is the only sniper rifle unaffected by the mod's penalty.
Was initially named "Reverse Tainted Mag" during the concept phase.