RE: Why doesn't my son want to use his new BB gun?
In today's society there are all sorts of subtle "brainwashing" techniques going on designed to teach kids that guns are "evil". I wouldn't be at all suprised to find out that he's been exposed to some of this anti-gun crap at school. It's all over the place and the gun control nuts know that the way to win in the end is to get their twisted message embedded into the minds of our children. In thirty years they will be running things and if they already come with a built in aversion to guns then the anti-gunners will have won. He might already have some pre-conceived notion from school that he shouldn't be touching a gun.
I'd make some suggestions along the lines of "why don't you bring your new BB gun outside, daddy'll show you how to shoot it". Make teaching him how to shoot a fun experience for the both of you. Quality time with Dad and all that.