Birdshot won't even take out an Iphone, don't suggest it is an "excellent home protection load". It is not. A heavy winter coat can stop bird shot. In fact, you're more likely to get bouncers with bird shot and take out your own eyes. #4 is the smallest shot to even consider. That's a Turkey load and while a Turkey is a bird, #4 is not considered bird shot. The best home load is #1 buck.
OK, let's do a test. You stand 15 feet (home defense range) from me in your winter coat and I'll shoot you with a 12 gauge using #6 shot.
In fact, you're more likely to get bouncers with bird shot and take out your own eyes.
I'll also be happy to help with the "bounce test" in a dry walled room. I'll shoot at the dry wall in your house with my 12 gauge. If I lose an eye I'll pay for the dry wall damage.
Look, buddy, you hit someone with a 1-1.25 oz. load of lead shot in a column still possibly contained in the wad at a distance of 6 to 15 feet, the distance most home defense takes place, traveling at 1100 feet per second, it will penetrate and stop the target, delivering every foot pound of energy that column of shot is carrying. At that distance, the shot acts as a unitary mass.
#1 buck shot carries too much energy per pellet and can penetrate through the target and a couple walls and injure children in the other room. This has been studied in ballistic studies. . . And the load of birdshot at close range is extremely effective. At longer ranges, the buck shot is better.