The firearms training course I took to qualify for my CCL would not permit the word "weapon" to be used. One reason not to use that word was in case you ever shot someone in self defense and you had to make a statement to the police or defend yourself in court. The word weapon has more negative connotations than say firearm, gun, pistol, shotgun or revolver. If you end up in court a prosecuting attorney would latch onto everything you say to use against you and if you call a firearm a weapon it suggests aggressiveness on you part, even premeditation.
I think this philosophy originated with the NRA.