6061, 5182, 3104, and 3004 are all soda can grade aluminums, Chain.
6061 is like, by far the most common aluminum you're going to find.  Oddly not the cheapest despite that, usually just because of it's giant use case.

7075 is your ""fancy"" aircraft grades, and it's not at all required to use that for firearms parts, it's just that the mil spec, and the TDPs call out for it because of the former usually.
You can get away with whatever pot metal shenanigans you're trying to get up to, that you won't tell anyone about, with 6061.

If you're melting down a bunch of soda cans tho, please remember that your resulting pot metal is not going to be ANY of those grades, but a very inconsistent mess of something.