Originally Posted by cyphertext

The thing is that they are not "all together"... they are all in close proximity, but it is not one single mass. Take a load of birdshot and shoot it into ballistic gel at 20 feet. Then take a slug and shoot it into the ballistic gel at 20 feet. I guarantee that the slug will penetrate further as it is truly one mass. At 20', a plausible distance inside a home, that is almost 7 yards. Bird shot out of my 18.5" cylinder bore has left the shot cup by the time it gets to the target. Cheap, unbuffered buck shot has also and makes a pattern about the size of my fist. It isn't one hole at that distance.

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I know that there have been cases where birdshot stopped, or even killed a person. However, there have been cases where it has not. The gel tests require 12"+ penetration before a round is deemed to penetrate RELIABLY to reach internal organs. Bird shot simply doesn't do this.