Copper solid sabot slugs is what I use, a well placed shot will bring them down fast.
I use a 12ga but I see they make them in 20ga too, there good out to about 150yds.
I don't know about you, but 99% of my hunting shots come within 50yds here in S.W. IN.
Shotgun Ammunition - Shotshell Slug - Premier Copper Solid - Sabot Slugs