Wild boar CAN be very tough animals. Even small yearlings can run away for miles after receiving a hit, that wasn't properly placed. I'd say it's 90% about bullet placement and 10% about bullet quality. But, as it happens many times with drive hunting, bullet placement on running game can present a serious problem, especially for the hunters that are not well used to this kind of hunting. And as for the big keilers, if they're not hit in something vital by a proper caliber and bullet, you can just forget about finding them. I've been present on many trackings with tracker dogs and we rarely managed to collect them in the end. I've heard that in some countries they don't even bother to track them, because it's considered a waste of time, as the chances of finding them are small. Anyway, these are just my observations. If nothing vital is hit and we don't collect them in the first few hundred m, we usually have a serious problem finding them.