Not happen to my new P90 (MARUI), as I did worry this before buying it this year, but it seems that MARUI have improved this problem, all my P90 mag (bought this year) without any problem in jaming. Most important is you need to make sure BB entry part of the upper body is clear when loading the mag, and you also need to load the mag properly, then your P90 will work very well without any jamming problem