Lung shots kill by the deer drowning in its own blood. The lungs are full of blood vessels- think a tree, with the main pulmonary being the trunk, then going into all the branches.
If the bullet punctures the main artery blood loss will be very rapid. Put the bullet further back into all the branches, the blood vessels are much narrower and hence takes a lit longer to bleed out. A punctured lung is a pretty survivable event if it either self seals with clotting or you add a wound dressing.
The reason why animals have all their vital organs towards the front on the chest cavity protected the shoulder muscles, bones and ribcage is to protect against puncturing injuries to thr major blood vessels. This causes rapid death, especially if you also take out the major bundles of nerves.
And roe deer are a small target and it doesn’t take much to be a bit off target, and at 200m bullets are already loosing quite a bit of velocity and thus on impact will cause a narrower wound channel, hence the need to ensure the bullet is closer to the centre of the killzone and major arteries. But given most stalkers probably can shoot a 2” group at 100 when we talk about first round hit after you have stalked into something, are lying with a rock sticking into your side on a slopping hillside and your heart rate is up, such a group opens up to 4 to 6” at 200, so even if your shot is perfect, naturally dispersion of bullet can cause you problems. Wind - 10mph feels like a gentle breeze, doesn’t affect at 100, can cause a few inches drift at 200.
And even perfectly shot deer run. Nature has an incredible tenacity for life and I have had roe run 100 yards having been shot through the shoulders with the heart obliterated. Usain Bolt can cover 100m in a bit under 10 seconds. A deer is at least twice as fast as a sprinter so can cover an awful lot of ground in a few seconds.
As you get more experienced you will realise that longer shots generally result in a more difficult and longer follow up, and that taking them vs trying to get closer or waiting fir a better chance is often the easiest option. Once you have spent several hours with that horrible sinking guilty feeling of a wounded whilst search clear felled timber covered in braken, nettles and brambles on 45 degree slope in the ****ing rain and dark you will come to realise this.
