1 shot, then trigger disable for specific time. 500ms to 2 seconds adjustment range maybe to simulate cycling the pump. This gets rid of the multiple trigger pulls per ball.
You could also set a "hopper size" to simulate tube feed, etc. Example: every tenth shot there is a 5-10 second trigger disable (to emulate swapping tubes or filling a box hopper). Or you could have a selectable "max" ball count for ammo restricted play. Essentially disabling for LONG periods (think minutes). It'd need to have a power cycle reset prevention though.
Just some quick thoughts.