If you have money go for the
TM P90 mags - Works 100% perfect with great fitment
Echo1/ACM P90 Clone Mags - Works 100% as well but may exhibit a few problems
The only difference is that the retention spring for holding the BBs in the Echo1/ACM mags tend to be a bit weaker and BBs and can pop out if agitated, 3/4 mags I bought had this problem. Also these clone mags don't feel as robust a body as the TM ones but still work well in Outdoor engagements, I always go prone squishing them and they still work.
Possible solution for it I would say put in a little spacer or a stronger pint size spring if you can find one. I am unsure if it will work but just an idea on where to start.
- Pistolero Steve