I too have been hunting for quite a while and have had my share of bang/flop. When I have seen this occur, it is on unwounded, unsuspecting game, or a hit to the central nervous system. If you can manage a lethal heart/lung shot on an animal that is unaware of your prescence your odds of bang/flop go up. Shot placement on my deer is normally behind the shoulder double lung, high heart.
The last one to go flop was quartering away from me at about 75yds head down casually cropping alfalfa from an open field with 40 or so of her freinds. The bullet entered behind the right shoulder, destroyed the spinal column just forward of the shoulders and exited behind her left ear. Easy to see why the flop happened once I opened her up. The head down feeding posture was responsidle for the CNS hit.
I have had clean broadside shots with only a rib hit and both lungs gone reslut in flop 3 times. All were strict broadside on browsing, unaware animals. One was busy licking a branch over his scrape when the lead hit hide. That one was a muzzle loader shooting a 240 gr .44 cal hornady XTP at about 1750fps. He dropped at the shot, went still, with his legs in the air and then relaxed and drooped. I kept expecting him to get up so I stayed put with my reloaded MZ trained on him and waited. He stayed put!
I rolled one like a rabbit one time with a 30/06. He was definitely aware of me and running broadside quartering awayto get some distance between us when I put a bullet into the spine just behind the shoulder. Quick shot in a "holy crap" situation. Big deer coming out of nowhere now running,BOOM, now rolling, totally back end over front end. A finisher in the neck was required.
It goes on and on, but I can say if there is any theme for me it is in the state of arousal or lack of it that will play a part in how far a deer may run when hit. Most often a deer will react like it was struck on the hind end with lightning when the bullet lands. A high bronco kick from the back end sometimes accompanies a heart shot.
The deer that went the farthest for me was a buck I had been persuing for a couple of months throught archery and muzzleloader seasons into rifle season. When I finally got a shot at him in the clear he was well aware of me having come out from behind a bush and spotted me before I noticed him. He was frozen in place broadside at about 100 yards, waiting to see what I was up to back in his bushy hideout. In the dim light of the overcast snowy morning his antlers blended completely with the scrub he stood in front of. At first I was unsure if it was him or not but after a few minutes of standoff, he began to move forward with a halting step and I instantly made out his headgear ahd readied the shot. At my slow movement he again froze and turned his head slightly towards me. At the shot he put his head down and ran for all he was worth. I mean RAN!!! I hit him perfect. Double lung with the top of the heart completely cut off and the major vessels disconnected.
If not for the snow I would have likely never found him. He dove into the rabbit bush and I gave him a couple of minutes then followed up. He went through stuff so thick I was amazed he could ever get through let alone at the terrific pace he was going. I had to crawl under branches so low it defies explanation how he got under but he did. Blood sprayed in a fine mist out both sides of his trail in the fresh snow so I had little difficulty following. What I was unprepared for was how tough the going would be. A rabbit would have been very safe in this thorn twisted hell! After a few dozen yards on this trail he left the trail at a right angle and went through some uncharted bush to where I found him a total of about 140 yards into the thick tangle. With the wound he was packing I was gob smacked to think how far he went and what effort he went through to get somewhere that I could not get to him. If the snow had not been there to show me the truth, I would have had a much harder time recovering that buck, if I ever found him in there.
So, bang flop happens someitmes but never count on it and remember that when a Whitetail knows he is dead, he will sometimes be capable of burying himself in the nearest thicket to an amazing extent before the lights go out. IF you know you hit him, don't give up looking easily!