I use a 22 pistol or rifle with subsonic HP, one shot back of the head. Aim just above the axis, where the spine and skull join. At night I blind it with the spotlight or my streamlight so it can't see me coming up from behind. I have also done it with a Beretta 950 25ACP. Worked just as good as a 22.
Just be aware of what's downrange and plan accordingly.
Yeah, it'll flop some.
The United States already has a national gun policy. It's called the Second Amendment.
The NRA is my union.