Really cool mechanic! I'm typically not the biggest fans of these types of games because I often find that the best strategy is to run and spam bullets, but this idea solves both of those problems! It makes the game interesting– I enjoyed it quite a lot!
One thing about the mechanic that I noticed is that I felt disincentivized to shoot from long range. I think the close-range shots make for exciting gameplay, but I wish there was some kind of reward for sniping someone from across the screen! Maybe doing so could spawn an extra bullet for you?
Great game overall :D