Our correspondent from Hobbiton, John Shirley, informs me that he has shot a Level II-A vest with a 12-gauge shotgun using 1 oz. slugs, and although the slugs did push the vest material about two inches into the target (broken ribs) they did not break through the material--but only if you miss the trauma plates, which apparently stopped 'em cold. Shows what I know--I didn't consider plates. I didn't think most patrol officers wore them.
So, if you're keeping track, it's actually very hard to get a "silencer" legally in Sweden, and a police officer's vest will stop a 12-guage slug, at least the 1-oz. vaned kind I use in a smooth barrel. I wonder whether John tried the saboted slugs, which would have much less frontal area? None of this is a big deal really, just technical details (I don't anticipate a need to shoot through body armor any time soon, and I haven't lost an confidence in my 12-guage) but I know more today than I did yesterday, and that's always good.
Standard slugs will not defeat common level 2 body armor. I know this because I have tested it, at about 2 meters. (Unless hitting the trauma plate, you will have a section of armor about as wide as a small maraschino jar pushed at least 2" into the target, though. Certainly more "impactful" than standard 00 buck, which didn't even dent the railroad tie backstop.
.223 will penetrate, at least the front side of the vest, and probably most of the "body". .44 Magnum will sometimes penetrate at least the front armor. .45-70 300 grain SJHP at about 1650 fps will blow through the front armor, railroad tie, back armor, and keep on truckin'.
Vest tested was a 10-year old Second Chance.
The point stands despite my sloppiness. Notice that the calibers that penetrated--.223, .44 Remington Magnum, and .45-70 Government, all predate the widespread use of personal ballistic armor. They were designed for penetration, yes, but none of them were designed to defeat body armor.