Mike, it is not terribly uncommon to see a Smith gun with two sets of barrels and each barrel be marked with a different steel type. Russ Ruppel for instance, owned an A-2 16-bore with one set of Whitworth and one set of Krupp barrels; and I've seen other combos like Nitro and Armor, etc. Old tight-fisted shooters could save a lot of money by opting for a lower grade set of barrels fitted to their gun. Barrels were priced at one-half the cost of the grade of gun; so, if a shooter had a $100 Grade 3 with Crown steel barrels for instance, a replacement set of Crown grade barrels was $50. If he opted for a set of Armor steel barrels fitted to his gun, he would only spend about $25; and, as Armor had a great reputation and $25 was a lot of money, this made cents but I've never understood why Hunter would sell barrels out of grade (needed the sale I suppose). What is unusual in this instance (this post), is that this one set of barrels features tubes of two different steel types; one of Nitro and the other Crown.