I'm a beginner at this. I shot two last week with a Tikka .270. One went down with a single shot in the shoulder, but he ran about 50 feet. The second one took a shot through the shoulders, turned and ran towards me and took two more head on before he dropped. It looked like a shot went into its mouth and exited above its rear leg. Both were about 120 lbs. Dad said the .270 too small, too fast. Range was about 60 yards.
So the reason I ask about using shotgun for close range is because the .270 seems to be better for long range.
I also have an M1 Garand, which might prove to be just the ticket.