As for them running on a little bit after they've been shot, who knows? They could have been lamped last year and not shot at, but are still wary of the lamp, their adrenaline is at full pressure, they're bound to have enough muscle power to go those few yards until they drop.
It's hard to explain
I shot a fox with the 12g last winter from about 30 yrds and
he took off running,he ran to the nearest ditch and half way up it he came tumbelling back down
Dead as a doornail.
He must have ran -90 yards,