High speed photogate readings and hardware interrupts (Help Needed)

Projects Programming
5 
      buttonState = analogRead(photosensor) <  700;

I find code like this rather annoying. That the sensor reading is less than 700 has nothing to do with the state of a button.

Don't use names that require thinking.

int buttonState = 0;         
    if (buttonState != lastButtonState && buttonState == HIGH && AmmoCount>0) {

buttonState is NOT a boolean. Don't use it like one.