"If a gun, for instance, isn't smartpropped already for the character I'm using, I'll never get it into a hand."

 

yeah, thats probably the best example of something that is difficult to manipulate with the built-in Poser dials :(
for something like a gun, i usually use the poser manipulator gizmos (rotate, twist, move) while rotating the view around the character to roughly position/rotate an object into place. then once its roughly there, fine tune it with the dials.  it often helps when doing things like this to set the poser workspace to multiple viewports.

get in the habit of saving off hand poses (ones that you make, or ones from figure poses youve loaded) into your own hand pose library. that way when you need a hand gripping an object, or resting flat on a table or thigh you can load a similar one from the library and youll only have to do a bit of tweaking, rather than remake it all from scratch.