I was just watching The Terminator (1984) last night and when the cyborg attacks LAPD Central Division, there are a number of officers that are able to respond with M16's. I imagine at that time those rifles would have been from SWAT inventory, but since it was fictional I won't concern myself too much with it. I believe it was the North Hollywood shootout that precipitated the widespread adoption of the M4 carbine as a regular patrol rifle now often carried in lieu of the Remington 870 shotgun. No doubt M16 and M4 rifles had seen patrol duty in some places before and that shootout wasn't the only factor that led to the increasing popularity of them today. I reload and shoot 6.5 Grendel in a bolt action gun intended for medium game hunting and in the low volume of fire of hunting it's probably going to have a greater effect than 5.56x45mm. I don't have an AR-15, but I suppose if I got one it would also be chambered in 6.5 Grendel. I might have even thought at one point that the military should think about adopting 6.5 Grendel because of how much more awesome it is compared to 5.56, but there are a few good reasons why that's not such a good idea. Performance with Mk262, Mk318, and M855A1 are a lot better than with Grandpa's M193. In most circumstances where the military is using M4's with 5.56, the ballistics are good enough, magazines have higher capacity, soldiers can carry more of it, and someone can carry an alternative like 7.62x51 without everyone needing to. The suitability of equipping soldiers with 5.56 makes the most sense when you start thinking about equipping most soldiers in a squad or a platoon with it rather than just thinking about individual soldiers on their own. For an individual, the difference in the volume of fire might be negligible, and so the potential ballistic advantages of alternatives look worthwhile. Multiplying the increased volume of fire by a squad or platoon, however, could give a substantial advantage to the smaller cartridge. Whatever advantage Grendel or Blackout or SPC or SOCOM or any of the other alternatives have, it's not a huge one and not without trade-offs. Another obvious reason the military shouldn't abandon 5.56 for some ballistically superior cartridge is because of their existing investment in 5.56 rifles, magazines, ammunition and the supply chain behind them. But none of these arguments apply to law enforcement. Patrolmen don't fight as a squad and certainly not as a platoon size unit. They're far more often alone or with a single partner. Departments don't keep an inventory of rifles, magazines, and ammo that fills warehouses. So what is the rationale for the far greater popularity of 5.56x45mm rifles in law enforcement versus alternatives like .300 BLK, 6.8 SPC, 25-45 Sharps, 458 SOCOM, 450 Bushmaster, 7.62x39 or 350 Legend ?