I had a quick look thru a fully moderated .410 the other day and though the barrel was drilled down its length in several places for the expansion of gases , it still had normal type baffles in the end just like a .22 silencer only bigger.
I am looking to buy a Hushpower type fully moderated 20Bore.
Based in kettering, Northants so anyone with one at a reasonable price and not too far away please throw your hat in the ring.
Regards.
May consider other calibres
Cheers