I'm out in Wyoming every year for two months and trust me an antelope can probably walk 5 mph and 10 mph is not even close to what they can do when spooked. Try 40 to 50 mph for short bursts and at least half that speed for a long time.
I understand that. Have been around quite a few.
Reality is OP might not have even hit the one he was aiming at. And in some states shooting into a herd is actually illegal.