I have never tried it but by looking at the round I will firmly say NO, The diameter of the 7.62x25 is way to big to feed from the magazine. And do to the more complicated design of the P90 mag you would have to redesign the feed ramps and follower not to mention maybe a insert for the shorter 7.62 round.
762x25 can be had for between 10 and 15 cents per round. The 5.7x28 bullet is too light, and the ammo is way too expensive. The 5.7 won't ring steel well enough to be used in a rifle match. I think a caliber conversion to 762x25 would sell like hot cakes, as it would allow PS90 owners to play with their "baby AUG" w/o worrying about ammo prices. But it's just a pipe dream ... Chris
I highly disagree ... 5.7 ammo is the only ammo that I know of that HASN'T gone up in price in recent months. For example ... what I pay wholesale now for some premium ammos is what I used to retail it for. 5.7 has stayed at the same price point regardless of all other ammo prices increasing.
Also, as was said by FN Man elsewhere in this forum, 5.7 is some of the least inexpensive rifle ammo available.
It's very important to remember that all 5.7 ammo, including civilian SS195 and SS197, is PREMIUM ammo not Wal-Mart FMJ's. Try buying a 50 rd box of PREMIUM 45 ACP for $18 these days.