It's gotta have some aluminum in it to fill properly. Pull tabs, soda cans and aluminum foil will work. You don't get up to the melting point of AL, but it rather "dissolves", than melts, into the alloy. It's harder (not impossible) to do with an aluminum mold (since zinc does dissolve aluminum), because you gotta work pretty hot and risk soldering your mold closed.
It also helps to enlarge the sprue holes to make it easier to get lots of zinc in there while it's still hot. Remember too, the sprue is gonna be
lots harder to cut. When you do get the bullets,
if you managed to get the voids and wrinkles out..... they will be an oddball weight and so you'll have to make up your own load data. Also, they will be at 30+ bhn and won't grip the rifling, so you won't gain any meaningful practice from shooting them.
Trade it to ShadyGrady for lead. He'll trade even and you can keep enjoying lead.
