Rotometals sells Zamac3 alloy, 96% zinc, 4% aluminum. I worked up a full bore shotgun slug that came out at 477 gr from a custom mold that I can safely shoot from a rifled barrel 12 ga @ 1700 fps and 10,000 psi. The same mold produces a 975 gr lead slug. I can hit you in the face every time from a rest at 100 yds from my 87O. Needs to be an iron mold. Works great for that application and no, zinc will not hurt your steel barrel. Coming up with a suitable load for a such a light bullet could be a challenge though.