There was a cop in Portland that mistakenly loaded a round of buckshot into a less lethal shotgun and shot a crazy guy with it. If you look at the internal report it's an almost unbelievable series of little things that went wrong, and it added up to two lives being ruined. The whole thing could have been prevented by visually inspecting rounds, but it highlights the dangers of having humans use a LL system that is capable of firing lethal ammo.
With the availability of 37mm launchers, pepper balls guns, and Tasers, I don't see any good reason to deploy a LL 12 gauge. I get that money doesn't grow on trees, but LL 12 gauge is false economy. The cost of one little mistake will pay for dedicated LL systems many times over. Portland paid $2.3 million bucks for one round of buckshot. They could have bought a Taser for every officer on the force and put 100 37mm launchers or pepper ball guns on the street and still had money left over. Never forget the guy pulling the trigger is the one facing prison, not the idiots who were too cheap to buy the right equipment to begin with. SWAT can have 40mm to play with and it makes it impossible to accidentally load a 40mm gas canister in a 37mm launcher and pop someone in the chest.