MAG Brand M4 Mid Caps (Real Finish 190 rounders)

[Mausturm]

Hey all,

I recently procured these mags for my King Arms M4A1, and for some reason, they cause a massive Air Leak with my M4. I tested other brands such as TM Mid Caps, and the FPS that my M4 chronoed at was 400. When I use the Mid Caps from MAG, it's 250-260 give or take. Only when I fire off an assortment of rounds does it return to normal. Anyone know what might be the issue here? Or did I just get kidney punched by the airsoft gods?

Thanks,

Mausturm