Projectile Weaponry seems to be a term mostly used in conjunction with role playing games to describe that set of weapons which fire some object using a mechanical device, i.e. the object is not projected by human force.

I believe the role playing connection comes from the fact that in the real world we do not have the contrast between laser guns, guns that shoot pure force blasts, etc. We have to rely on good ol' slug throwers, and thus there are not these category distinctions one finds in the settings of science fiction and role playing games.