No cannon opening.
Maybe I described it wrong; the shots are not bullets, though.
Here, maybe something like this is what we both had in mind.
This is when the weapon is used at short range and out of melee range:
When the user performs a slash, it'll fire something like you see above.
When the user performs a punch, the blades will fire long energy/plasma bolts.
It's a work in progress, though.