I've been replaying CMBB lately and there's a sound effect that always confused me. When some light tanks fire (I can't name a specific vehicle right now) you hear about half a dozen thunks in a row. These are light tanks with smaller guns. It is the main gun that's being fired, not the MGs, but it sounds like rapidly firing 5 or 6 shots. It only looks like one actual shot, both visually and the effect of fire. But you hear multiple discreet sounds.

So what's going on there? Is that a bad sound effect, or if that's a realistic gun sound, why does it sound like that?

Perhaps it is the sound of the breach being cleared and casing ejected? Which specific vehicle? I'd like to check it out.

Turns out they were Panzer IIs and after a little research I found that they had fully automatic cannons. They had 20mm autocannons, so they did actually rapid fire several shots in a burst. So the sound is an accurate representation of an automatic main gun.