I don't know if it would still retain lethal capability after going through an exterior wall. As Dave said, buckshot loses steam quite rapidly downrange -- the round ball shape is aerodynamically inferior to something like a boat-tailed rifle bullet so it will lose kinetic energy much faster.
The problem with taking a shot at a perp at 50 yards with a buckshot-loaded shotgun is, as you state, the other 8 pellets that don't hit the guy. I wish I had some wallboard to run some penetration tests with buckshot, maybe that will be my new project.
But the best thing to do is, if you must take a shot at a goblin at 50 yards with a shotgun, is to transition to the slug. The problem is, civil liability (and possibly criminal liability) will attach to you if ANYONE downrange gets hurt. And we can imagine too many realistic scenarios where someone gets hit and injured -- it's much better to hit the guy with a slug than risk sending 8 "flyers" down range.
For example, say we run our tests and determine that a 00 pellet does not retain lethal capability at 50 yards after hitting an exterior wall. So we see a goblin at 50 yards and let loose with our buckshot. What if some guy is out in his lawn raking leaves and gets hit by a stray pellet? What if the exterior wall is missed, a window is hit instead and then someone on the inside gets hit and seriously injured? What if one of the pellets goes through an exterior wall and then hits a small child or a hemophiliac?
In all those instances, you are liable civily, and maybe criminally for any damage caused to property and person. There is a famous tort law case which every attorney learns in law school about a kid who sustains serious medical damage from another kid who merely tapped him on the shoulder during class (the first kid had some sort of medical condition). The moral was that the tortfeasor "takes his target as he finds him", so the second kid was held responsible for all damages caused to the first one -- even though all he did was tap the other kid on his shoulder. So even though we only nicked the hemophiliac, if he dies -- hoo boy are we in trouble.
John, correct me on that case if I'm wrong, I never did well in my first year law school classes.
This long-winded reply is not a flame, as you asked a very intelligent question. Only the conscientious person would have wondered what happens to those other 8 pellets, the careless person would have let them fly without a second thought. We are accountable for every projectile we send downrange, so the question of overpenetration with buckshot at 50 yards is very relevant.
My answer is that since tort law (and criminal law, probably) will hold us accountable even though we anticipate from our penetration testing that 00 buckshot at 50 yards will not harm someone after going through an exterior wall, better to switch to a slug instead. As John Farnam said in his text "The Farnam Method of Defensive Rifle and Shotgun Shooting", the answer to overpenetration concerns is not reduced power ammunition, but shot placement.
As usual, not a legal opinion or legal advice.
Justin
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Justin T. Huang, Esq.
late of Kennett Square, Pennsylvania
[This message has been edited by jthuang (edited August 03, 2000).]