I was in a group discussion about what is the best shotgun HD load. One person said #7 shot. I said 00 Buck. The last guy chimed in with #4. Here is his rational.
#7 - not enough effective stopping power
00 Buck - over penetration. Will probably end up with several BBs in the next room or next house
#4 - Compromise between the two. At inside the home distances, has enough stopping power yet will not penetrate a wall should you miss.