RE: Winchester Fail Safe Bullet
I don't know. The last 2 Elk I shot with .300 WM 185 gr Failsafe Winchester premium both big animals stopped right in their tracks like with shots right behind and below and shoulders. I told 2nd shots just to make it quick for them. There definitedly was sizable exit and mucho blood, so they weren't going to go too far.
Maybe it is the combination of your choice of caliber and a lighter slug. Many variables to say in a situation.
I didn't see you say how far the animal ran and if you were up a chasing from the first shot. Even whitetail deer will go a long way with lethel shots if they are pushed hard. Grandpa Victor would used to say after shooting an animal (taking the shots you can while in sight) sit down for the time it would take to smoke a pipe (or have a cup of coffee). Then get up and track it. You give it time to lay down and bleed out if you don't push it. Otherwise, it may run for quite a ways and if the exit wound isn't bleeding out well, clog up and you may not catch up to it.
I don't know your situation though. If you got the animal, give thanks. You did well.