When it comes to a tactical rifle for SWAT or patrol work, I prefer the .308 and other larger caliber weapons for their increased energy and superior ballistics. Were I to arm myself with a gun of the AR platform, I’d choose one chambered in the original caliber of the breed, the .308. After all, the earliest variants of the AR were designed to chamber the round. The 5.56mm guns came subsequently, chosen for their higher ammunition capacity and lighter weight in both weapon and ammo. The rest is history.
In law enforcement, we don’t “hump” rifles and ammunition for miles and miles on foot through jungles and rough terrain, nor do we sustain the large number of rounds exchanged in military firefights. We typically drive to the scene of the fight in a patrol car or SWAT vehicle, and don’t have to carry them far. In this scenario, it makes sense to carry a rifle that packs a harder punch, and hauling high quantities of ammo isn’t nearly as big of a concern.
If over-penetration is your concern, let not your heart be heavy. Modern ammunition designs such as those found in Hornady’s TAP (Tactical Application Police), Federal’s TRU (Tactical Rifle Urban), or Extreme Shock’s BTHP, control penetration for practical police purposes.