Pump markers are manually actuated between shots.
Stock class markers substitute constant-air for a 12-gram powerlet and hopper for a feed tube.
Magazine designs include the RAP4/Tacamo (more-or-less interchangeable), Dye DAM mag and Kingman mag.
They are almost always magazine-fed and powered by 12-gram CO2 cartridges, though hopper and constant-air adapters may be available.
.50 cal is common among low-cost mass-produced designs, as the projectiles only require ~1/3 as much energy to fire, compared to .68 cal.