There is a product that I started using about five years ago. It's called Strong Arm. What I like about it besides cleaning off rust, is it's lasting protection on preventing rust to come back. For long term as well as short term storage, I use it sparinly as a little goes a long way. There are a lot of equally good products and this is one of the best. It won't hurt your stock. ...
For leather, I use a product called Black Rock.
Be Safe !!!