This observation is based on 34 years of hunting deer with a .54 ML, some years exclusively hunting with the ML, and with deer limits rising to 12 per year.
All this is to say that I'm not baseing my opinion on 1,2 or 3 deer.
So, many years ago I cast all my own projectiles out of the softest lead I could find. If I couldn't score a deep scratch with my thumbnail I didn't use that lead for round balls but it was good for pistol bullets. Most deer I shot didn't go very far and a lot of damage was done by the soft lead expanding.
Now fast forward to when someone didn't return my casting equiptment and I started buying swaged round balls. Over a few years I noticed a pattern developing; deer were running farther with good shots and there wasn't as much internal damage being done. This really got my attention when a doe ran over a 100 yards shot through the heart.
Upon examination there were identical entry and exit holes indicating little expansion. But on the inside there was very little damage done almost as if the internal organs had been pushed aside instead of torn.
So take it FWIW but I think the hardness of the projectile plays a large part in this equation but is often overlooked in the quest for speed.
Once upon a time I shot a mule deer buck through the lungs at 140 steps (I step pretty close to a yard when I mean to) with a 50 caliber Rb. The deer made about 40 yards. Not much in the way of damage. Just a hole through and through. I have shot MD buck at 30-40 yards with a 54 with 120 gr of FFFG GOI. Deer ran about 50 odd yards. Pretty big holes through the lungs, about the size of a silver dollar, like they were cut with a large arch punch.
I shot a similar MD buck with a 38-40 Colt Lightning Magazine Rifle 37 gr. FFFg under a 180 gr cast. Not real soft or too hard. Bullet made minimal wound channels in the lungs, diameter a little bigger than a pencil. Deer piled up in about 40 yards though it gave no indication of being shot. I have seen MB bucks shot with 7mm mag with lung tissue hanging out the exit wound run 200 or so.
I have seen an Antelope buck that was grazing in the herd when shot run 50+ with a hole large enough to take out 3 ribs on the exit side.
I knocked a cow elk down with a 54 RB by breaking the humerus. Ball then made a large hole in the aorta. Cow went down at the shot at about 80 yards, then got back up as I was putting the patch and ball to the muzzle and ran about 50 yards.
My son shot a WT doe at about 80 yards with the 6.5x55 and she piled up on the spot with a heart shot. Heart shot deer usually panic run. This one dropped like dynamited.
I shot one at 300 yards two years ago the bullet breaking the humerus then messed up the lungs, passed through the heart sack but only bruised the top of the heart and exited. Deer ran about 100 yards and went butt over tea kettle as she passed from sight. A buck was hanging around her and I waited a few minutes for him to leave on the off chance the doe might be better off than I thought and I did not want her getting back up if the buck spooked. After walking about 300 yards I found her head still up and I then head shot her.
The same season, same rifle, I shot a doe IN HER BED though awake with her head up at about 180 yards, breaking the humerus and taking out the heart. She got up and ran about 30 yards and piled up.
Based on my experience I do not believe the wound channel is a deciding factor. Yes, a large wound channel will usually result in shorter travel. But this is not always the case. Nor will a conical bullet even a blunt one at BP velocities make a great deal of difference. I shot a few deer with a 40-70 BN sharps with a soft FP PP bullet under 300 grains. It seemed to be a good stopper. But I also shot an antelope with it with more typical results. So? I DO know that a SOFT (1:40) FP bullet in the BP loaded 40-70/40-90/45-70 works better than a RN or semi-pointed at 1:20 alloy.
Sometimes the deer falls dead, sometimes it runs off, I have not been able to determine before hand what will occur regardless of the firearm or bullet used.
This is the .662 ball that killed the doe previously mentioned. Note it has hair imprints of the ball. I cannot imagine any 45-50-54 BP arm making a would channel larger than this ball did RIGHT in the vitals, the heart, yet the deer ran as far or farther than other deer shot through the lungs with far less effective projectiles.
There is no constant here. Its a "your mileage may vary" thing. I get the idea that deer in some areas are easier to drop than others (?) but how would one tell?
I hear what I assume are perfectly valid accounts of deer falling to the shot more often than not with loads and shot placement very similar if not identical to what I have experience with yet MY deer tend to run off.
Is it genetic? I know that a lot of hunters in the east have the opportunity to shoot more deer than I do so the experience level certainly appears the be adequate.
My point is that if the deer did not fall over with the RB its extremely unlikely that some other projectile from the same rifle is going the change this. But one would have to shoot the same deer to "prove" anything. So "proof" is nebulous.
I EXPECT the deer to run off after being shot. Its the norm where I hunt.