ok heres how it works.
1.the ball valve being in the open position(no chamber pressure)
2.the ball valve must start to be closed,befor it is fully closed the ammo will drop in through the opening in the top of the valve
3.as the valve is closed a burst disk can be inserted through a hole on the bottom of the valve
4.when the valve is opened to the fully open position the chamber can be pressurized (or there can be another valve between the ball valve and the chamber)and when the disk bursts the ammo will be shot down the barrel.
5.on repeating these actions,when step 3 is reached the broken burst disk will fall out of the bottom hole allowing you to replace it.
Burst disk made easy.
Basically, the burst disk would be part of the ammo, sounds easy. I posted an idea while back, just use the ammo in the ball valve as a piston, a potato would probably seal well enough, the potato and the air would only leave the barrel once the alve fully opens.
"There isn't a problem in the world that can't be solved by the proper application of explosives"