the duty rounds mentioned in that article don't seem to make much sense to me in this topic. They talk alot about rounds that were made to have better penetration, yet that is niether a quality desired for HD situations, nor is it a shining quality in the .223's intended purpose, nor of the round itself.
Get yourself some highly frangible ammo like Hornady TAP. If not, then at least keep along the lines of something like 55gr or higher. With normal or frangible ammo, overpenatration should be an unlikely problem - especially with TAP.