Our good friend Andrew at GY6vids loaded .223 Remington cases into 12 gauge shotgun shells and fired them into ballistic gel. When he told me about the test I was skeptical that there would be much penetration at all. I thought a lot of gas would leak when they are fired, I thought they would have no accuracy at close range and that they would tumble so much penetration would be minimal. Turns out I was wrong!