How positron cannon works?

Usual behavior of positron cannon is that it shoots one per 1-1.5 second. And it is hard to say what exactly time interval to wait for 2nd shoot.
Though, I've noticed that sometimes it can should twice in a row with a quite small interval 0.25-0.5 seconds. But I could not realize how does that happen and how to make it shooting more frequently.
Also, I've noticed that positron cannon can accumulate up to two charges. It looks like if you press and keep pressed LMB for more than 1-1.5-2 seconds, shoot from the positron cannon is twice more powerful.
How to be sure when cannon is completely charged and can shoot with HIGHER power?
Any advises or information on this cannon is welcome!
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Seethrough Cannon - Watch exactly how a cannon works and fires
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