I don't know anything about Astra shotguns, but you might want to look at fowler from Laurona. They had chrome-line barrels special highly oxidation resistant surface finish and 1370bar proof (Boy Scout type steel shot proof mark) making them especially suitable for shooting steel shot. I know some years ago they invested a lot to bring out series produced SxS rifles in medium cals like 9.3x74mm, but I'm not sure if they're still in business or not.