Look guys, if anything will stop a lethal aggressor, it will penetrate walls if you miss your target. Quit worrying about what happens if you miss and practice so that you don't. While birdshot (so named because it's meant to use on itty-bitty critters normally used for food) can be lethal to large, highly motivated critters at extemely close range, that isn't a range you want a lethal threat to be at when you engage.

Don't bet your life, or the lives of those you love, on what's termed "less lethal" specialty ammunition like bean bags and rubber bullets. You may be expecting incapacitation, the other person may not have read the ads and fail to react in what you may feel as a proper manner. Also, people have died after being hit with those. As noted, it could be argued that the use of that type of ammunition indicated that you did not feel you had justification to use lethal force and any resulting death is manslaughter.