Tokyo Marui VSR-10 original MAG is also 30rd.
You know,using Marui original MAG,you can't shoot the last 1 BB.
So actually you can shoot 29rd.
DEEP FIRE's MAG, you can shoot 30rd perfectly but after shooting the last one,a magazine plunger will be sticked out from MAG.
So without notice,you push the bolt,MAG will be got a damage.
It's same system as APS-2 or Classic Army M24.
Feeding BB is really smooth.No problem.