I will say bullet construction may have more to do with it than some of the other factors. I have had many bang flop kills when using 150-180gr Nosler BT's, usually 180's as it's my normal load. But I do seem to have less effective results when using a tougher bullet, like an Accu-Bond or Partition. I think it's possible to go too soft as well, such as the A-Max, as it has done excessive damage in my experience, though I used a 208gr A-Max from a 30-06 on deer.
But still, I have seen far more very fast kills from the .25cals than I have any other round of similar size up to .30 cal. They just work. You can't shoot one in the arse and have it die, and yes shot placement does still matter. But it has always been my experience that a .25 will produce an almost immediate fall of the animal if you put the bullet anywhere near the generally accepted "vital area".
And please don't take this out of context. I am not saying it's the "best" deer round, or that others can not be effective. Only that in my nearly 16 years of hunting and seeing others use .25cals that they have produced many very fast kills. Others here have many more years in the woods than I, and I understand that as well. But even still, many have also seen the same thing from the 25-06 that I have, a round that just does an exceptional job of taking deer size game.
There will always be the guy who uses one and can't shoot, and no it won't make you a better hunter or kill more deer with bad shot placement than any other round. But if you can shoot well, the 25-06 will very rarely leave you disappointed. And more often than not, it will leave you wondering how it made the deer fall so fast.
And just to be clear, I am writing this as a staunch supporter of the big bore rounds. I do not use a 25-06, or anything even close in size on deer. I use a 30-06, a .35 Whelen, a 45/70, a .500S&W and a .50 cal BP muzzle loader, as well as a 20ga slug gun. So I am not writing this as it's my "favorite round" or that I even use one, because I don't.
I write this after watching several others use them and seeing the proof with my own eyes that they do the job of taking deer very well. I don't understand why, because I feel my big bores should do better, but they don't. At least not until I get to the 45/70, and then I am limited in range.
I do have high hopes for my Whelen, and as I have only used it once with great results, I am optimistic that it will be my "bang flop" round. The tried and true 30-06 does do very well, but I always strive for better, hence my going bigger. I don't want to "give in" to my father's nagging that the .25cal. is better, but I do want to show him there are other rounds that will drop deer just as fast as a .25.
I hope my .35 Whelen proves to be even faster.
Kenny
Maybe since it's a semi-auto I can slip in a second round really fast without anyone noticing, just to be sure. ;D