Had this happen to me this year during muzzle season. Was using my Sidekick with 300 gr. XTP sabots and 100 grs. of BH209 powder. This buck came into my area at about 55 yds. and I hit him with a quartering towards me shot. He didn't even react, but walked about 8 steps and just froze. I reloaded, but couldn't get a second shot. I got from my stand and got to within about 35 to 40 yds. and took a quartering away shot and he still didn't react, but walked three steps and fell over and died.
When I field dressed him I had given him two killing shots. On the first he didn't realize he was dead. When he froze, I think he was just in shock. Two good shots, but the reactions were very uncommon.
Like I said, it was a similar situation, but with different results. Both those XTPs, tore him up good. Smashed his heart and both longs. Very good bullet and one I use for my hunting handguns.