RE: .22
I'm assuming you are referring to a .22lr rifle (as opposed to a 22caliber centerfire or .22mag etc)...Given a good glass and an accurate rifle, I'd probably be willing to take a shot at 75yrds, 100yrds maybe in perfect conditions...a head shot that is, penetrating to the brain is pretty easy, the problem is getting your bullet to hit what you want. Getting a Marlin 60 or Ruger 10/22 to hit accurately enough to ensure a head shot at 100yrds isn't very difficult given the right glass. 75yrds isn't an estimation of capabilities, I know for a fact that it's capable of this-I've done it, 100yrds I haven't, but based on the fact that on the four different occasions that I've taken 66-81yrd shots with .22lr on yotes and produced exit woulds, I'd be quite confident that 20-40yrds later it'd still do the deed. That range isn't for everybody, or every rifle, hitting the head of a yote at 100yrds isn't hard, hitting the brain is, the rifles I've done this with shot 2MOA or less.