An old H&R single shot with ,you guessed it ,low brass bird shot. Of course it was shot from only 2-3 feet away but it dropped em like a ton of bricks. Also scared the hell out everyone in the kill room because they never warned anyone first
What's the point? Everyone knows that birdshot is lethal before it has a chance to spread out, especially if it hasn't left the shot cup yet. Similar to shooting a single projectile, though penetration would still be considerably less than a slug----but apparantly enough for cows.