Eightbore you are right to like your reloads. One half ounce shot is 218.75 grains. So your slightly over weight load is maybe six to eight pellets over the norm. But what your slightly heavy load does is I bet raise the pressure slightly and you get loads with less velocity variation shot to shot. In the .410 getting every shell to be the same helps because you have less margin for error. Or maybe you can use those extra eight pellets better than all the rest of us. They say you only need one lucky hit and you have eight. Still I'd have to read the regs to see what the margin is for loads. I think you are safe.
