In relation to other Democrats, Bernie Sanders is more moderate in gun control measures he would like to see called into action. However, it is my opinion that he truly desires a more controlled process for purchase and ownership of guns as he does not agree with the majority of Republican politicians on their policies. His self-proclaimed D- rating with the NRA positions him on the Democratic side of the debate.
I truly believe that Bernie Sanders' beliefs are genuine. Throughout his entire campaign, Sanders chief concern was creating policy that would benefit and support the American people, quoting Lincoln, saying, "we want a government of the people, by the people and for the people." Sanders' beliefs absolutely come from a place of truth and a genuine care for the American people.
Several House Democrats staged a sit-in to show their support for gun control legislation. Bernie Sanders participated in this sit-in as well. Sanders, however, has not been a strong proponent of gun control legislation in the past. In fact, he has remained steadfast in his support of the Second amendment. In short, Bernie Sanders' beliefs about gun control are more political than genuine.
Sanders joining the House sit-in is just a political move. He knows he has no chance of getting the Presidential nomination, so he's trying to get popularity other ways. The whole sit-in is a ridiculous waste of time. Changes take place through votes, not through pouting if you don't get your way.