I think too often politics is separated into "right v. left." This is a terrible way to label, given the authoritarian/libertarian split amongst conservatives and liberals.
I can easily understand an authoritarian liberal instituting more gun control. It would fit with their general view of the state's role.
I cannot easily understand a libertarian liberal supporting the same policy...unless one frames the debate in a very strange way.
I think the gun control question is more authoritarian/libertarian than liberal/conservative in nature. Oddly, the DNC took the authoritarian side, and the GOP took the libertarian side. I think this is odd, given the stances on other civil/human rights discussions.