Wow!!! Lots of really bad/misinformation on this thread.
The 5.7 x 28mm FN was produced as an easy to handle, lightweight, close quarters weapon, that had the ability to defeat body armor without the concern of over-penetration (that can happen with the 5.56NATO)
My reloading manual lists a 45gr Sierra sp, -max load- as having a muzzle velocity of less than 1600fps. That's LESS THAN HALF THE VELOCITY OF A COMPARABLE .223 load. Regardless of BC. The fn simply does not have the powder capacity, it's a tiny little 22cal cartridge, by any measure.
Sure a well placed shot with any gun at close enough range will take down game, but should you really recommend that sort of thing?