The WW's I've sorted thru had markings in addition to the weight. "Zn" was marked on some, "Fe" on some others. I'm pretty sure that meant zinc and iron. The "Fe" marked ones were noticeably less dense than the others so that makes sense. Don't worry about the AL, P and MC markings. They denote application, not composition. I'm told that as long as you keep the pot temp below the melting point of zinc that they'll simply float to the top with the clips for easy removal. I kinda doubt they were using much zinc 15 yrs ago.
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Smokeless powder is a passing fad! -Steve Garbe
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My favorite recipes start out with a handful of used wheelweights.