if you don't want use a real gun get a paintball gun and use small clay balls instead of paint it'll drop some one quick and is accurate enough at close range. if you want to use a shotgun you can get rubber pellets. rocksalt, rubber slugs, bean bags, etc all kinds of less lethal nasties out there you can drop some one with
for a funny story a few weeks ago I see a racoon on my back porch so I walk into the kitchen and grab a bigass knife off the rack walk over to the back door about to get homicidal on a racoon and yank the door open with knife at the ready to my very suprised girl who was in the process of letting herself in she also scared away the racoon so I didn't get to stab it