Pretty easy to take apart a P90 (one of the easiest I've done).
Basically;
1. Take off bb magazine.
2. Push tab on top of receiver (usually covered by mag) and pull front of receiver off.
3. Take off back stock cover.
4. Remove screw(s) holding battery plate on inside of stock.
5. Remove plate.
6. Slowly pull out mechbox.
Ta Da!
That's it unless you want to take off hop-up mechanism then just turn it to align notches of hop-up with receiver and pull the entire inner barrel setup out. Pull off clip on hopup mechanism and you can then pull out inner barrel along with hop-up rubber.
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