The grasp and thumb dials give you a basic hand movement that closes the fingers, but for some weapons, like firearms you still need to get in with the hand camera and manually tweak the fingers using the dials. There's currently no collision detection in Poser so it doesn't know when something solid is encountered, in this case you have to judge where best to stop. If you change the tracking option to full you'll see the figure rather than the bounding boxes which will help a lot to judging when the fingers encounter an object. Don't worry about some collision because the fingers will naturally crush and appear thinner when grasping an item. All in all, I tend to use the dials almost exclusively for hand poses and will spend more time on the hands than the rest of the pose. But I've always found that full tracking when posing hands with/on/around an item is essential as it's all but impossible to judge by having the default setting active. That is only useful for broad movements where finesse isn't needed but speed and smoothness is.