Revolving chamber cannon.

those things can achieve rates of fire comparable if not exact to rotary cannons but only have one barrel.

in conventional weapons, they are lighter and have less taxing maintainance demands with the drawback of having all the heat of a rotary cannon and none of the spin assisted air cooling, which means you can't hold the trigger and laugh for 10 seconds because the barrel will melt.

overheating the barrel isn't an issue with a pneumatic spud cannon though....