With some 10th-grade metal trades skills, the guy over at Farm Craft brewed up an AR lower from 265 beer/soda cans.
Nothing really high-tech involved. He melts the cans down in his foundry furnace, first into muffin tin ingots and then pouring the molten recycled aluminum into a plywood and sand mold box.
Cutting off the sprue and machining out the billet, he threads and mills until he gets a relatively mil-spec receiver to which he drops in a LPK, attaches to an upper, and rips some rounds through.
Now if he could turn an AR lower into a can of beer, that would be magical.
Remember to recycle!