I don't think you'll be able to get a meaningful FPS if your two sensors are only spaced as far apart as what would be allowed in a jank silencer. Run a foot long silencer and then maybe you'll get an idea of what's involved. Not sure what the point would be, anyway. Before proper games, players shoot through a proper chrony.
As for being able to keep up with counting shots fired, what kind of ROF are you working with?