Targeting (chest) & Improved Critical

[Zerorevenge]

How exactly goes Targeting (chest) work in tandem with Improved Critical?

It only says that Targeting the chest critically-threatens on a 19-20.

Improved Critical doubles one weapon's threat range.

Does that mean that then, with Improved Critical tallied in (assuming the Targeting bonus gets added last), it becomes a 18-20? Or, does it actually double the threatened range [versus just adding one] in which it would become 17-20?

Looking for either a Mod's answer or just a general consensus. I just hit level 7 in my friend's campaign, and this dilemma came up. (as I'll be taking Imp. Critical at level 8)

...Especially because I have "Magnum" Cartridges (obviously house ruling, one of a few, like no Touch AC to hit.) which takes 30% more gold to make, and adds one to your critical range (as the original thought of a higher crit multiplier was _ridiculous_ to fathom).

Would I use the base gun, 20.
Then Improved Critical, 19-20.
Then Magnum Round, 18-20.
Then Targeting? Because then it could be [if it doubles] 15-20.
Or, if it only adds one (NOT doubling), 17-20.

-OR-

Should the Magnum bullet be counted last? Altering the math...
Base Weapon, 20.
Improved Critical, 19-20
Targeting, 18-20 or 17-20 (if it merely adds 1 or doubles like Imp. Crit)
Magnum Round, 17-20 or 16-20...

Huge Difference when you're dealing with a X4 Critical Multiplier, and a bunch of other players who thinks the Gunslinger is broken and whine constantly about it (Outside of the actual game)...

Thanks in advance to any help with the dilemma.

Hope that I don't look like an idiot and miss an obvious answer to this in the Gunslinger Test #2 PDF...

Also need the opinion on how to order the addition concerning multipliers...

Edit: I'm 99% positive that it's official that Targeting DOES stack with Improved Critical, I remember seeing that here on the forums earlier... In case someone's going to bring that up.

[SRT4W]

I was under the impression that things that increased critical range don't stack with one another.

http://www.d20pfsrd.com/feats/combat-feats/improved-critical-combat-
http://www.d20pfsrd.com/magic-items/magic-weapons#TOC-Keen

Ect.

Also here is the next from Targeting in the 2nd round play test.

Targeting (Ex): At 7th level, as a full-round action,
the gunslinger can make a firearm attack with greater
accuracy and effect. When she makes this attack, she can
choose part of the body to target, and gains the following
effects depending on the part of the body targeted. If a
creature does not have one of the listed body locations,
that part cannot be targeted. This deed costs 1 grit point to
perform no matter which part of the creature she targets.
Creatures that are immune to sneak attacks are immune
to these effects.
• Arms: On a hit, the target takes no damage from the hit
but drops one carried item of the gunslinger’s choice,
even if the item is wielded with two hands. Items held
in a locked gauntlet are not dropped on a hit.
• Head: On a hit, the target is damaged normally, and is also
confused for 1 round. This is a mind-affecting effect.
• Legs: On a hit, the target is damaged normally and
knocked prone. Creatures that are immune to trip
attacks are immune to this effect.
• Torso: Targeting the torso threatens a critical on a 19–20.
• Wings: On a hit, the target is damaged normally, and
begins to fall.

Torso says nothing about stacking.