If you don't disrupt CNS< its not DRT. Simple as that.
YOu can get DRT, IE dying in place and not moving, at other times but its not 100% reliable.
The inferior vena cava is the largest blood vessel in mammals, it is a very thin-walled, low pressure vessel that returns all of the blood from the lower body back to the heart. If you puncture it, you get an instantaneous/marked drop in blood pressure. Google Starling's Law to understand this.
A Berger, placed on or right behind the shoulder, will most often produce enough fragment to puncture the vena cava or the aortic arch, which will have the same result but probably take a few second longer for B/P to drop enough for the animal to go down.
You are correct that "speed kills", that makes modern bullets perform, but once you have enough for the bullet to work (IE 308) more ain't any better.
