Brass is softer than steel. It will wear out instead of the barrel. Aluminum is softer toobut the aluminum oxide on the outside of the rod is very hard and abrasive. They make sandpaper from aluminum oxide. The bronze bearings are made from crystals of bronze formed by pressing and heating just enough to fuse them together but not melt them. This creates a structure full of tiny holes that hold oil like a sponge. A totally unrelated product.