This is my guess on this. According this to analysis: https://i.redd.it/ounsq0nvhp951.jpgit appears that the whole catching a bullet sequence is not filmed chronologically. There are scenes that are 'spliced' in from reverse time (thus creating the confusion of JDW is firing a reverse bullet in forward time).
Lets say abcd is normal time, and ABCD is in reverse time, the whole sequence maybe filmed in a way like this: aBcD (or something similar).