I really prefer M193 out of 14.5/16" barrels, since it takes a 2650 FPS threshold for 5.56 to tumble and break apart at the channular. M193 will do this reliably out to about 200 meters from a 20" barrel, 150-160 meters from a 16" barrel, and 100 meters from a 14.5" barrel. M855, on the other hand, will only do it to 150 meters from a 20" barrel, 90-95 meters from a 16" barrel, and 50 meters from 14.5" barrel.

With that said, however, it is nice to have penetrator rounds in your kit. Realistically, if I use it, it will be under the 95 meter limit. past that range, it is time to escape and evade!

Good article on 5.56 fragmentation ranges on Ammo Oracle

http://www.ar15.com/ammo/project/term_fragrange.html