Firstly, it's possible to make Called Shots as a half-action if you're inside a suit of power armour with working auto-senses. Thus, you lose only the +10 bonus.

(Presumably, it would be possible to ask your heretek of choice to scavenge a PA helmet and include its sensor suite into another helmet if you don't like leaving footprints in concrete)

Secondly, that -10 you retain from the single shot after maxing out your Shot-Calling abilities can theoretically (best case) translate into 10 points of additional damage if you're shooting someone in Power Armour without a helmet and thus get into Crit territory where your Crack Shot kicks in.

The fact that there exists some more-or-less unobtainable (for most people) gear that offsets some of the penalties for the Called Shot action does not make the initial observation any less puzzling. 

Shooting at a small-sized target that is part of something larger is much harder than shooting a similarly sized target that is not part of something else.

I find it hard to accept that shooting a flying skull is easier than shooting somebody in the torso.

I conclude this pedantic rant by reverting to the original Dark Heresy rules for this particular action.

Darth Smeg said:

Simple - when shooting at a part of something larger, there are other parts that can (unconsciously or deliberately) get in the way of an attack. That isn't the case for a single smaller target. It's not the size of the target that matters, it's the necessary patience and inherent awkwardness of trying to guarantee a shot to a particular part of a larger target. Remember that the rules assume for a standard combat situation that  everyone is inherently trying to defend themselves and avoid making themselves an easy target; with that in mind, I don't see the restrictions as being particularly unreasonable.

Beyond that, from a strictly mechanical perspective, the penalty needs to be sufficiently significant to make it an optional risk - the penalty and the necessity of it as a separate Full Action are both to ensure that it doesn't just get used at every opportunity without a second thought.

As for benefits... there is one that isn't quite as clearly stated, as it isn't covered in the rulebooks. Called Shots can be used to target crew and passengers of open-topped vehicles. With that in mind, I don't think it's too much of a stretch to assume that a Called Shot is the action for a GM to require for any similar sort of "shoot out a particular piece of a given target".

It's odd - I've never heard any complains about Called Shots until this thread; indeed, there was a thread on the Dark Heresy forums a while ago that was calling for the bonus damage from the Accurate quality to be restricted to Rogue Trader-style separate action Called Shots.

Darth Smeg said:

It's not really the same action, though.

When you make a normal attack, you're attacking at the first opportunity of getting a clear shot. Sometimes, that's a head if you're lucky with your timing, but sometimes you just take a shot at the arm or leg, because those were the first things that lined up with your sights. Aiming in this context doesn't mean so much lining up your sights better as it's focusing more of your attention on the opponent, predicting his movements and seeing more openings.

When you're making a called shot, though, it's headshot or bust. You don't care how many times the guy was in a perfect position to stuff his chest full of lead, you're trying to get a clear shot at his head, no matter how much the bastard keeps waving it. And it's always a more difficult shot, because it's hard for an experienced shooter to not follow the movements of the whole body, but all one needs to miss a headshot is the target suddenly ducking a little. Aiming in this context means, again, taking more time to line up your shot, or perhaps waiting for the half second the bastard keeps his head still.

Cifer said:

Personally I would preferred a ruling more on the lines of "Called Shots are only possible with Standard Attacks" if their intention was to prevent called shots with full-auto and the like. Personally I don't have a problem with that being possible, but I can see the problem later on when you might as well make all attacks be called shots as you had negated all the penalties (I don't see the problem in melee, as at least there you have had to close with the target, exposing yourself, but with ranged attacks it would basically render all but full body armour useless. With my suggested ruling it still would be vs single shots, but not burst fire, encouraging more "single shot between the eye" duelist types). At least with my suggestion you would have to forfeit the possibility of extra hits.

At the moment I could rarely see the point of called shots (and making it essentially a -30 now makes it even less appealing). The penalty is significant, and the difference it makes is usually minor as most enemies that they are publishing at the moment seem to have near identical armour across their entire bodies, and though the critical table changes where you hit, the boost from that is minor compared to the almost certainly much more significant damage boost you would get from other attack options. Either you spend your entire turn making a "Called Shot", at a penalty or -20, or you can make a "Full-Auto" attack at -10, getting the chance of multiple hits (increasing damage) and you still have a half action to do something else with (including aiming, turning it into an attack at +/-0). You can improve your chances with talents, but they still don't strike me as terribly appealing with called shot being so hopeless in the first place.

"It's odd - I've never heard any complains about Called Shots until this thread; indeed, there was a thread on the Dark Heresy forums a while ago that was calling for the bonus damage from the Accurate quality to be restricted to Rogue Trader-style separate action Called Shots."

- I have had an issue with it since the Rogue Trader change, I just haven't said much about it. The change to attacks in Black Crusade just made it even worse, as most of the attack options became half-actions meaning the justification for choosing called shots became even slimmer. The Accurate damage boost you have to spend a full turn carrying out to get the bonus (half action aim, then standard attack) but you get a good boost from it (as you say, a boost that some possibly argue to be too good, but at least there is a very obvious justification for using the whole turn doing it).

I'm just doing

Called Shots are the Dark Heresy version. As in, -20BS/WS to attack a specific location. You CAN autofire/swift attack a specific location, but it still follows the Multiple Hits Charts (IE: five shots from full auto on Called Shot: Body won’t all go on the Body). Note that you cannot use Called Shot for All-Out Attack.

Because you know what? When you fire the first shot, it"ll hit the head. The rest just won't. I don't see anything wrong with that.

Actually, the second hit will also hit the head.

But I agree: The benefit of headshots (or Called Shots in general) is the possibility to avoid armour, and IF the person has spent the required XP to gain the Talents to negate the penalty for Called Shots, then I say Good on him.