The major components in "Gun Metal" are :

$\mathrm{Cu}, \mathrm{Zn}$ and $\mathrm{Ni}$

$\mathrm{Cu}, \mathrm{Sn}$ and $\mathrm{Zn}$

$\mathrm{Al}, \mathrm{Cu}, \mathrm{Mg}$ and $\mathrm{Mn}$

$\mathrm{Cu}, \mathrm{Ni}$ and $\mathrm{Fe}$