Action Army Fast Reload Drum Magazine for the AAP-01 & AAP-01C (and maybe your Glock...)
 
Designed by Action Army for their AAP-01 and AAP-01C pistols, this should also fit most Tokyo Marui clone pistols as well.
 
Better yet, these are lighter and smaller than the WE / Armorer Works Drum Magazines and balance out the AAP-01/AAP-01C nicely.
 
These are fitted with a safety blow-out valve to protect the magazine from over-pressure, so the highest pressure gas you can use is Green Gas. 
 
Called a Fast Reload Drum Magazine due to the unique way the front loading door opens to reveal a large opening for filling. A further advantage is the magazine can sit on its back while being loaded, so no tricky balancing act requiring three hands to ammo-up!
Now add a 'flash' magazine loading system and it can be wound in seconds - no more turning the huge clockwork winder on the front!