It doesn't make sense why a character with a level in gunslinger and a level in "monk of the empty hand" can't use a two-handed firearm as his quarterstaff, since according to the APG a monk of the empty hand uses "a two-handed weapon as a quarterstaff." so the two-handed firearm should therefore be able to be used as a quarterstaff in melee combat. A staff magus gets the quarterstaff master feat as a bonus feat at first level. Why can't a character wield it with one hand utilizing a feat he will have with a weapon he already treats as a quarterstaff in melee combat. It isn't like I'm asking for him to be able to fire it with one hand with the quarterstaff master feat, I'm asking if he can hit someone with it, in melee, one-handed and still use his spell strike.
I'd sure like a legitimate reason why this can't be done. I understand that it is an improvised weapon, but a quarterstaff is a quarterstaff, improvised or not. If a character has special training to make any two-handed weapon a quarterstaff, then that character should be able to transfer that training over to other classes and utilize quarterstaff feats. its like saying i can't use rapid shot to throw a pile of rocks with my throw anything feat if i used I obtained the feats from two different classes bonus feats.