I just got my WA M4A1 CQBR shot it a couple times to make sure it worked. I filled the mag back up with BBs and put it away. The next day it wouldnt work after I filled it with gas. After examining everything I found that the piston on the mag that the hammer hits had no pressure behind it, I could push it in all the way.
So i began looking for extra mags and of course there impossible to find just my luck. If anyone had the same problem or has info on how to fix the mag let me know.