[Dynamo]

here's the thing about pot metal, it's an aluminum/zinc alloy. the reason why it is used so much in our airsoft guns is really simple, it's cheaper to cast. plain aluminum is tough, light and considered soft (thats why it's tough), but to cast parts out of it, only a few options are available. alum can be sand cast, plaster cast, or injected into a steel mold (die casting).
where as zinc is much lighter, but also much harder (really brittle) and has a much lower melting point than aluminum. so it can be die cast in aluminum molds instead of steel (much cheaper to make).

when you mix the two together, you get an alloy that has a much lower melting point than the aluminum alone, so it's much easier to cast. so instead of using steel molds for casting parts, they can make the molds out of aluminum and save big $$. the draw back to using pot metal is that it's more brittle than aluminum so it is prone to breaking in high stress applications.

one of the advantages of alum/zinc alloy is that is more wear resistant than aluminum, which makes it good for certain mechanical parts, mainly where parts will be sliding/rubbing. it should be avoided anywhere where parts would be hitting each other.