Not safe to shoot slugs out of a full choke. I did a bunch when I was a kid before I knew better with my .410, but that doesn't mean it was safe. Too much constriction at the muzzle.

00buckshot probably isn't safe in a full choke in a .410. Full choke restriction should be 0.035", so .410" - 0.035" = 0.375". 00buck is 0.33", only leaves 0.045" for the wad, which I'm betting isn't nearly enough. Not as bad as a slug, but not great.