Seems that it's just wrong or simply unclear description of per bullet effect itself, not the ability. I belive that for every per bullet effect game caltulates build-up percentage by amount of damage dealt compared to your bullet's damage. For example if you got 10 bullet damage but dealt only 5 due to distance reduction, effect will be filled only by 4%. So just keep in mind that it could fill less, but not more. Funny part is that melees counts as bullets too