Thanks for your input so far.
I don't necessarily want to kill the dogs- with snake shot, or anything else- they're beautiful dogs and it's not their fault the owner is a dumbass. I figure a snake shot hit on the rump or side will be enough to deter them from our property.
I also don't want to use a standard ball because you have to aim *really* low at short range, and especially on a moving target that's asking for trouble; plus, I figure a snake shot miss is less likely to harm our chickens than a ball miss could.
People light off fireworks (or, they could themselves be shooting BPs, hard to say) in our neighborhood all the time, no matter the day or season; either it's allowed/condoned or people don't know or care if it's fireworks or a BP shot and so nobody makes a call about it. My wife has fired three shots from a .22 in our yard to scare off a (different) pack of dogs one time, and there was apparently no call made then either.