Owen ~
Been thinking about this since you posted it, and have a couple thoughts.
First, I think I agree with you that there is no
universal "natural" grip angle. You make a compelling case about the way the human wrist is designed, without a locking point unless the wrist is at the limit of its rotational ability. So far, so good.
However, I believe there may be a "natural" grip angle for any individual person. You kind of touched on that, a little bit, when you said it was a matter of what any individual has practiced shooting. I would not stop there, though. I think I would say that the most comfortable grip angle depends upon the individual's muscle and tendon flexibility, and the exact geometry of one's wrists,
as well as the individual's accustomed wrist motions (which may include how much the individual has shot firearms which use a specific grip angle).
One of my best buddies is closely related to an octopus in his wrist flexibility. Doing jujitsu with him is lotsa fun, because it is darn near impossible to get a wrist lock on him even when you do everything exactly right.
Husband, in contrast, has the least flexible wrists I've ever noticed on anyone. You can lock his up pretty well by looking at him cross eyed.
So best buddy has no trouble whatsoever adjusting to various grip angles. His wrists are flexible enough that no grip angle stretches any of his wrist or forearm tendons, or tightens his forearm muscles. So he can "naturally" point guns with lotsa different grip angles without thinking much about it.
Husband, on the other hand, has exactly
one grip angle that works for him, and he had to practice bunches even to find that one comfortable. His tendons are tight enough that putting
anything in his hand stretches them. There really is no "natural" grip angle for him -- just one that he's taught himself to habitually use.
Two extremes, admittedly. But perhaps gives you an idea what you're up against when you say there isn't a "natural" grip angle. Each individual may have an ideally-comfortable grip angle, but they don't necessarily have only one. And
taken as a whole, humanity does not. Further, the individual may have a preferred grip angle based on any number of things -- his own natural wrist geometry, years of previous shooting and getting accustomed to a particular angle, or because he is accustomed to some other repetitive wrist use besides shooting.
Now it gets even more complicated: toss in the size of the grip. (See photos at
http://www.corneredcat.com/FirstGun/TryOnGun.htm if you have a hard time visualizing this next bit...)
I have come to suspect that how well the grip fits your hand
might also affect how you perceive the "naturalness" of the grip angle and how comfortable that angle is for you. A grip that fits your hand perfectly might allow you a more comfortable range of grip-angle possibilities than one that does not. This would be because a too-small or too-large grip generally forces the wrist to curl slightly to the left or right, which
might in turn limit how comfortably you can flex your wrist up or down to cope with a slight change in grip angle.
Dunno if this is clear enough, or if I should keep talking. What do you think?
pax