Well it does't work like that. That is if you have 20% accuracy then you will need to shoot five times the amount of bullets that you need to kill. The accuracy is the number of hits that you get divided by the number of the total rounds you have shot. Some times you shoot a whole mag without getting a hit just to suppress the opposition and some times you are spot on. So what you did is you assumed that you have to shoot, every time, 5 times more bullets and so you need 5 times more time to kill thus giving you enough time react.
Well I have news for you. It does not work this way.