I know a lot of people don't agree with me, but, personally, I don't like the idea of shooting steel jacketed bullets, especially in an old classic vintage double rifle, because those older rifles simply don't have the much improved modern alloy barrel steel available today, which is way more durable than the older barrel steel. Common sense will tell you that steel jackets being pressed down into rifling grooves cannot be a good thing; the more you shoot them, the less good thing it is. But what about the protective guilding metal shield over surface of the steel jackets, doesn't that protect the barrel steel? Guilding is nothing more than an extremely thin copper alloy covering over steel jackets; it can't, and doesn't do much in protecting the barrel steel. It does protect steel jackets from rusting. These are reasons why Hawk custom bullets designed their bullets having PURE, SOFT copper jackets, way softer than guilding copper alloy of any kind, so that they would be easier on older vintage double rifles. Obviously, they would also be easier on modern alloy barrel steels too. As with most everything, shooting steel jacketed bullets is a compromise; shooting few of them may be tolerable, to you and to the barrel, but the more you shoot, the more that you have to be wearing the rifling lands to some degree, though some guys don't want to admit the truth. If you are willing to wear your barrel rifling to some degree, though wear might be small, if you shoot few of them, to gain the benefits of the steel jacketed bullets, shoot away. If the virtues of shooting steel jacketed bullets outweighs the risk of wear, shoot away. Otherwise, avoid their use as much as possible. If someone tries to tell you that their use will not wear barrel rifling at all, I simply don't believe them.