Just as important as what others have said.
No matter the maker,action type,or gauge.
Make sure that you have the right ammo for the task.
Birdshot is for cheap training/manual of arms use and hunting small game,never use it as a defensive load.
Make it a point to stock up on buckshot and slugs in your chosen gauge.
Any well made 12,16,20,or .410 with the right ammo can be a very effective anti-personnel weapon,as long as the user does their part.