First off I'm lazy about writing my Congressmen on gun issues and I shouldn't be. A friend introduced me to this site and I would like to encouage everyone to use it.
Put in your zipcode and it shows who your elected offical are. Click on their name, then click on "contact". After you can click on "contact by webform" and it list the current issues. Click the issue and you have a pre typed letter or you can type your own. Put in your name, address and click send. That simple.
I don't know if we will ever know how much good this does but contacting our Congressmen is about the only thing we can do to voice our opinions to the people voting on these issues.