Looks like he's doing all he can to get rid of that.
He’s competing with Hillary, he has to.
He was a reliable anti-gun vote when his vote mattered, and a “pro”-gun vote when his vote didn’t matter. Instead of saying that his voting record is “mixed”, it would be more accurate to say that he had the voting record of a panderer.
He actually gets a lot right with this:
Mental health emphasis.
Gratuitous, desensitizing violence in the media.
Political environment that encourages winning by shouting down the other side.
I’d suggest addressing all three of those area first, and seeing how they work, before implementing even more gun control laws.