Frame Dependent rate of fire of a gun

There is a lot of code, so please ask if you require it. The video of the issue:

Impossible to give specific help without seeing the code.

Nonetheless using Time.deltaTime and such accordingly is generally how things are made frame-rate independant.

Plenty of info in the manual: Unity - Manual: Managing time and frame rate

I solved it. Turned out that invoke is frame dependent (at least at 20 fps). So I redid it with booleans, timers and Time.deltaTime.