What you experienced is the cooling down effect
Most of the time when you continously shoot the mags it gets colder and colder and soon you loose less shots and its less consistent. Sometimes it might just fart out all the gas like a WE Gas pistol, but not all guns fart out, only cheapo clones do.
Tokyo Marui Hicapa magazines are compatible with the gun so you should get those as they tend not to get so cooled so fast like other clone guns.
So its quite normal to get at least 1.5 magazine clips like my TM Hicapa 5.1 gets at least 1.5 to 2 mags in before losing out which is like 45-60 shots
- Pistolero Steve