[hiredhand]

the P90 is a very small bore centerfire rifle. 5.7mm IIRC, with a smaller case max-dia than the 5.56mm/.223

Good point, but I've seen AirSoft guns that you could NOT tell from the real thing.... case in point, here's my paintball gun. With the low profile hopper, it's difficult to tell from an M-4. :-) I put the 200 rd hopper back on it because "fashion" loses it's appeal after the first couple of times of being "scourched" by teenagers on the opposing team. :-)

[Dead Corpse]

Yowsa! That looks neat! My Christmas wish list is already maxed out for this year...

There is always next year though...

[King Prout]

I'm passingly familiar with several Airsoft models of the P90.
Most of them have opaque magazines.
The only one that I know of that has a full-simulation magazine (dummy rounds visible) (by Tokyo Marui) has a full mag with no stack variance at the feeding end.
If you look closely, you will see the double-stack vary into feeding file in the image in question.
If that is a model, it is a DAMN slick one.