What determines the AP used per shot while in VATS?

All things being the same it seems I can use a standard 10mm gun and get about 5 shots in, but go with a fully automatic weapon and I'm lucky to get 2 shots (and full auto shots generally do less damage per shot). So Rate of Fire doesn't seem to be the factor, unless it's reversed. Is it weapon weight? What?

Thanks.

It may be weight; scopes also factor in --- tack on a scope, and the # of shots per VATS cycle plummets to maybe 1 - 2 or perhaps 3 if you have a ton of Action Points. My 10mm seems to be able to fire like twenty times or something insane compared to two or three I get with my sniper rifle. I don't remember the guns actually ~listing~ how many AP they consumed per shot. I completely blank on whether previous games had that kind of info available on-screen.

EDIT: As for why I would want that info --- often I will "double tap" one tough foe to make sure he will go down and then move to a second foe only to find out that I don't have enough action points to make a shot, so I have to "back up" and remove a called shot to the first guy so I can make a shot on the new guy. And with VATS no longer ~stopping~ time, this can be vital time wasted.

dunno, but good question.

Fallout Wikia shows only AP cost for a couple Institute guns and all the melee weapons.

http://fallout.wikia.com/wiki/fallout_4_weapons

One "shot" with an automatic weapon is actually a burst, so that would explain why the cost is high.

As to your original question, each weapon has a base AP cost, which is then modified by... stuff. Perks, mods, drugs; anything COULD affect the cost, mechanics-wise.

I get 16 with Deliverer fully specced, 6 with Overseer's Guardian strongest .45 semi-auto receiver with red dot sight, 3 with specced Gauss Rifle with compensator.

It's weird, the Deliverer stops at 16 but over 1/3 of the AP bar is unused.

10 Perception, 12 agility with my combat get-up.

16 is the maximum number of shots regardless of AP.

So if I add an auto receiver to a 10mm, the VATS shots will drop from 5 to 2 because the auto VATS shots are 2/3 shot burst? I'll have to pay closer attention to that as I couldn't tell that before.

Still if I'm wanting to play a pistol gun slinger it would be nice to know which gun gets the best damage/AP used in VATS. The .44 does great damage but is another one that seems limited in it's shots in VATS.

One factor is the weapon type and another factor would be the weight of the weapon.

Pistols have low action point costs because they are small and light weight which makes them easy and quick to aim. Rifles are heavier than pistols so by default, it cost more action points to use them in VATS. Heavy weapons like mini-guns and fatmen consumes the most. They are big, heavy and unwieldy which take more time (and action points) to aim.

The weight of the weapon would be another factor even for the same type of weapon. If you have one 10mm pistol that weighs 5 and another that weighs 6.5, the heavier 10mm pistol would cost more action points to fire.

I am going to assume the weapon's fire rate also plays a factor. The higher the fire rate is the less time in between shots which means less action points. So for example, a .44 pistol has a fire rate of 6 while the 10mm pistol has a fire rate of 46. Due to the faster rate of fire, each shot of the 10mm pistol should cost less than each shot with a .44 pistol. But this is pure speculation...

also, chambering each round. The .44 is apparently just single action because the animation shows cocking before each shot. which means slower.

same with big weapons, gotta re-chamber those rounds!

I would think that means semi-auto and full auto should get most shots in AP.