Head shots aside, I understand that the brain contains enough oxygen to support 10-15 seconds of purposeful action; an awfully long time if the bad guy's purposeful action is ending your life. Unfortunately, unless we train for head shots, that's the best we can do. But, a center-mass hit with a shotgun almost guarantees that the vital organs will be shredded, meaning that the 10-15 seconds is probably all the bad guy's going to get. With a lesser firearm, you may or may not hit vital organs, even with a perfect shot; especially a small caliber like .22. That means that 10-15 seconds may drag out into 10-15 minutes, 10-15 hours, who knows? That's also aside from the fact that .22 does not have sufficient power to penetrate the chest and organs and damage the CNS. A head shot, yes, but those are ill-advised in a home defense scenario. I've actually gone and done some research on the topic this evening, since I was interested in the discussion. A standard 2-3/4 shell with #1 buck may be even better than 00. It's got 16 pellets that fall somewhere between a .32 caliber and a .380 auto, and penetration in ballistic gel is just over 12 inches. That's pretty impressive; and once I get my shotty out here I think I'll keep it loaded with #1. Seven rounds of #1, assuming all pellets strike the assailant, means that poor bastard is going to have 112 .30-caliber bullet holes in him. If that doesn't cause a precipitous drop in blood pressure leading to unconsciousness and death, I don't know what will.