Right about 2000, G&H ran big ads in SSM for a cased shotgun w/accessories as a Christmas gift. Several members of my club purchased them. As I recall, right around $4200.00 maybe 3600 without the case and accessories. About 1 K greater than a shop Arrieta of same model designation.
Right after was the first I saw with a ring bulge after a SoDak trip. Then over time, people would post on various sites about them, asking what to do. Nothing to do.
They obviously sold quite well, because they are regularly available.
I would not run OTC heavy pheasant loads in a large shot through one.
While it's true the OP did not say what the gun's proof marks are, and if made after 1993? it could possibly bear steel proof marks, none of the guns I handled did.
The G&H kits I handled weren't custom ordered.
Who knows. Perhaps the OP is talking about a heavy fowler with triple steel proves. But at 6-8, I doubt it.
People are free to fire whatever cartridges will fit in their chambers.
It will fire steel shot.
