I have only shot a few deer, I am not a real experienced hunter. However one of them was shot with a Brenneke rifled 12 gauge slug. I was using a smooth bore slug barrel with rifle sights.
It was late in the day, I decided to snooze on the ground and the buck walked up on me. I reached up and aimed my Mossberg 500 one handed and shot the deer just behind the shoulder. I should have aimed further forward because the shot basically went low and diagonally through the lungs. The deer ran off.
I picked myself up and found pieces of lung all over the scrub brush. And the blood trail, looked like someone had taken a bucket of red paint and splashed the ground, on the sides of trees. Huge blood trail, blood on the left, blood on the right.
Followed it, and not more than 50- 75 yards away was the deer.
The entrance wound looked like a drilled hole. I mean the hole was about the size and shape of an egg. Huge. On the other side, intestines were hanging out the wound.
If I had hit something structural, like a shoulder, I am sure it would have flipped the deer. I tell you what, a big square chunk of lead puts a world of hurt on the target.
As for me, my side hurt for days. When I shot the Mossberg one handed, the gun recoiled back into my ribs.
I asked the guys at the weigh in station about the performance of slugs. They see about 300-500 deer a year there, and in this hunting area you have to use slugs or blackpowder. They were of the opinion that slugs were a highly effective projectile on deer.