What does "fire rate per weapon mean?"

[Snowbro's nice cream]

What does it actually mean?
What is the correct, unequivocal definition of it?
What exactly do the highlighted numbers in the following picture stand for?

http://i.imgur.com/oP6BuCK.jpg


Why does it drop to half three times (1->0.5->0.25->0.125) then proceeds to drop diminishingly twice (0.125->0.11->0.1)?

[Falquian]

With one gun you fire twice per second.
With 2, 4 shots per second

The max fire rate is 10 shots/second with 6 guns. It increases a lot with more than 4 guns, but 6 will give you the max DPS.

[Big Mad Wolf]

You mixed a bit up:

Shots per second:
1 gun = 1x
2 gun = 2x
3 gun = 4x
4 gun = 8x
5 gun = 9x
6 gun = 10x
7 gun = 10x

[Snowbro's nice cream]

This is very important news!
So from 3 to 4 SMG the fire rate increases by 100%, while from 4 to 6 it only increases by 25%!
Thanks a bunch, this is very precious information.

I also notice it scales pretty weirdly, for instance from 2 guns shoot once per second each and it's fine, but 3 guns shoot for a fire rate of 4 shots per second, meaning not only all guns don't get a slower fire rate, it actually gets faster?
And adding another gun will make it even faster?

1 gun - 1 shot per second, meaning it takes 1s to "reload"
2 guns - 2 shots per seconds, makes sense, every gun takes 1s to "reload"
3 guns should be 3 shots per second but it really isn't
4 guns... wow! 8 shots? Reload time drops to half!

But wait, there's more! Upon reaching 5 guns, the reload time actually increases, and increases furthermore with 6 guns!

This is especially important when working with a mix of different gun tiers. For instance having 3 TX and 1 T-10 SMG has actually a very similar DPS compared to 3 TX and 3 T-10!

Here's the math:

Assuming 1 TX = 2x T-10 in DPS

with 3 TX firing 2 shots/second and 1 T-10 firing 2 shots/second you get the equivalent DPS of 3x2x2+1x2 = 14 T-10!

On the other hand, 3 TX firing 1.6 shots per second plus 3 T-10 firing 1.6 shots per second give you a DPS of 3x2x1.6 + 3x1.6 = 15 T-10!

The difference is lower than 8%!