Two apps, actually. There may be more like them but these are the one's I've found. You tell the apps where you live and they generate letters to the appropriate officials. The letters politely but clearly state opposition to the wrongheaded anti-gun legislation now being discussed by the Congress.
From Ruger: http://www.ruger.com/micros/advocacy/takeAction.html
From S&W: http://www.smith-wesson.com/webapp/wcs/stores/servlet/Category4_750001_750051_787655_-1_757992_757992_image#
We have some voices on our side in D.C., even in the Senate. What writing letters does for you is to make it easier for wobbling congresscritters to wobble over to our side, and support stances like this well articulated précis by Senator Ted Cruz: