GTL 480 has a 480 cc Air Reservoir and the GTL 290 has a 290 cc Air Tank.
( Ironically, both weight approx. the same )
Aesthetically, they look a little different ... The most noticeable differences is going to be shots per fill and that the GTK 290 has a 10 shot mag (in 9mm) v/s the GTL480 has a 6 shot magazine (in 9mm) ...