Common usage doesn't make it correct. And I'd say it's only commonly used among people who just don't know any better. Calling something by anything other than its actual name doesn't make any sense, especially when you know its actual name. A clip is not a magazine, whether you like it or not. Communicating accurately is important.
Rest assured that I know the difference. Some words change meaning over time, slang developes and entire languages evolve or we'd all talk like Romeo and Hamlet. Some hairs only need to be split by people anxious to demonstrate that they know what a stripper clip is. Big deal.