Originally Posted by Phantom Power
You could always go with a technologically advancing paintgun theme.
Splatmaster > PGP > Bushmaster Deluxe > Mac-1 Annihilator > Autococker > Typhoon > Vector
Or something like that. Still keeps it having an old-school or vintage feel.
I think something along this line is appropriate, but do it with more common guns.
007, splatmaster, phantom, automag/cocker, spyder, whatever else would follow