Charlie I have been reading about wildfowling over in the U.K , probably the only place where 8 bores still see serious hunting . Apparently there was a company called Greylag in the U.K boring out these heavy 10 bores to make modern 8 bore boxlocks . They used a Kestrel 10 bore as the base gun .

Muzzles still have some thickness to them surprisingly , though if they are reproofed after boring I would think they are stout .