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?
sierra, is that out of a 4.5 inch test barrel or a 16 inch test barrel? you'd be surprised how slow 223 is coming out of a pistol length barrel. there are lots of carbine length rifles that increase the velocity a great deal. federal premium lists the same 5.7 bullet in both rifle and pistol velocity. the pistol gets very close to that you stated. the rifle gets over 600FPS faster. no mis information, just misreading.