until they come up with ammunition that's not classified as armor piercing, and start selling it in the states, you're going to have a hard time finding things to fire out of it. problem is, even the armor piercing ammo sucks for terminal ballistics. it yaws almost immediately in gelatin, and has very little penetration. which renders it useless except in something like a P90, where you can fire strings of several rounds in the same spot, no problem. in such an instance, the trauma and ensuing fleshular damage from that many rounds in a small area would be enough to incapacitate. and the armor piercing capabilities of the round suit it to rear-located forces. the ones that are only likely to be overrun by enemies with armor, because any others would probably die long before hitting the rear.
all in all, i know nearly nothing of the 5-7 (i'm not writing the damn name out), but have read plenty on its ammo. current research is being done on an FMJ and expanding rounds in 5.7mm, both by FN and by ammunition companies here in the US. hopefully, one will come up with something that performs, because the lower recoil and higher capacity that the round an its weapons systems offer is good. the ballistics just suck.