Metal feeders aren't the whole solution, though. I had one, hanging on a tree branch. The squirrels jumped up and down on the branch until the feeder fell to the ground and the top came off!
I now have a 'Squirrel Buster' feeder. It has a mechanism whereby if the weight is too much on the perches, it closed over the seed holes. It works for larger birds, too, like the dang starlings and grackles. Rats with wings, they are.
I've only seen my father shoot at two living things with his BB gun, a cat that was harassing ours(as in would chase out cats into the house, follow them, and then try to mark our walls) and the flippin grackles.
They keep trying to nest in our walls! We sealed the hole they were getting in through with sprayfoam insulation, then chicken wire, then more insulation, then a piece of sheet metal. It's been over a year and you can still find the buggers trying to get in!