Brass was more common. It is sturdy enough for some hard use. It doesn't take long for the brass to take on a dulling patina to become almost brown.
Even with the barrel still in the white, my Derringer Rifle with brass hardware does not reflect light as the white barrel has become gray and the brass quite dull.
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Now, my King's Musket is a different story. Brass was chosen for the hardware on the King's Musket. I am sure brass wouldn't have been selected unless it was suitable for hard military use.