I use 32 gram #6 shot 12 bore cartridges for pigeon shooting, with one of those the muzzle velocity is about 1300fps, not 400. Also it doesn't knock birds down by breaking their wings, it kills them stone dead as the shot pierces the body. This is at something like 40 yards, not the 30 feet quoted here.

Gloves wouldn't be a lot of protection at that range and I would certainly expect the pellets to do more than just break the skin!