Contrary to what some believe, this mod doesn't directly reduce reload times; it increases reload speed. The calculations are far different, and that can cause some confusion.
The calculation of reload time using reload speed as a variable is almost the same with melee charge speed, which is Base Reload Time/(1+ Reload Speed Bonus)
At max rank, estimate a ~29% reduction to reload times.
Stacking this with Quickdraw should reduce reload times by 47%.
The 10% proc chance bonus from this mod is smaller than the 15% from Sure Shot, which is already insignificant with the current system. It is recommended to only equip this mod if you need the reload speed.