When I got to her, she was definitely down, but still kicking and moving while laying on her side. I put a second shot right through her sternum to try to put her out of her misery. While I'm sure that second shot was more than enough, I did finally put a third a few inches away from the second and that one definitely ended her. I make note of this to say that oryx are TOUGH. When cleaning her we found none of the rounds had made it all the way through. The first shot was a few inches high, so missed the heart, but double lunged her and this would have likely been lethal... eventually. We found the bullet inside her skin on the far side. Tracking back from where she fell to where she was for the first shot, there was almost no blood trail to speak of. Just a few dots here and there in the dust. Certainly not something I would want to try to follow for any real distance. This is likely due to the fact that the round didn't exit, and her skin was practically a 1/4 inch thick. Again, they are TOUGH animals.
We chose to clean and quarter her out in the field as we did not have a hoist of any kind to get her into the truck, and they are very heavy animals, even without the huge gut pile. One of the rules for WSMR is you can leave the ribs in the field, but you must take all edible meat. I took the shot at about 1140 in the morning, so we had ample time to relax and take the time we needed to really clean her up good. I did make the rookie mistake of not going far enough back when caping her out, and later got the advice from a taxidermist to go half way back the ribs, that way you know you have more than enough. Live and learn on that one. Thankfully a good taxidermist can fix my mistake for a little extra $$$. After the hunt, we got one more email saying the success rate on our weekend was 75/81, or about 93%.
If you made it this far, thanks for reading my bit of bragging, and I hope you did learn something, even if it's just what NOT to do. I'd be happy to answer anyone's questions to the best of my ability, but again, this is just my personal experience, and it's based on a single hunt.