Chainfire works because you turn on guns as you fire (so they fire at different intervals), not because of a early fire bug that causes guns not to fire.
It makes non-firing guns fire in sequence when they can do so. Ex: make group1 all guns, group2 only the rear guns, then chainfire 2-1 while pointing forward and rotate around the back, group 2 guns will be staggered even though they didn't fire forward