"For some reason in British loaded cartridges the 2”” seems only to be found with 6 shot"

Several years ago I came across some 2" .410 Italian made shells loaded with 3/8 ounce #4 shot; these things were tiny and I purchased a box specifically for my B-I-L to use in his Stevens double. We chased bunnies with beagle packs at that time; and since he never missed, I was thinking these tiny shells might level the playing field. They didn't, he used those shells to go 5 for 5 on our next hunt; and I found it impossible to believe those shells could be that effective. So when we returned home I stepped off about 20 yards and placed a "target", a 20" x 24" cardboard box with marked center. My B-I-L then shot the box using one of those tiny shells, after which we counted the pellet strikes produced; the total was three. So I was right, technically those shells weren't worth a crap; but they sure were effective for him that day. Sometimes simply being lucky works better than being good.