Nate Silver breaks down gun ownership by political affiliation:
In 1973, about 55 percent of Republicans reported having a gun in their household against 45 percent of Democrats, according to the General Social Survey, a biennial poll of American adults. Gun ownership has declined over the past 40 years — but almost all the decrease has come from Democrats. By 2010, according to the General Social Survey, the gun ownership rate among adults that identified as Democratic had fallen to 22 percent. But it remained at about 50 percent among Republican adults.
He writes that demographic data "suggest that gun ownership will continue to decline among Democrats while holding steady among Republicans, further increasing the partisan gap." Relatedly, Enten takes a closer look at Democrats' gun control views:
Those in favor of fewer gun restrictions are winning the battle because they are breaking into demographic groups that normally vote Democratic. Romney took only 36% of the vote in urban areas, but 46% of urbanites were for minor or no gun restrictions. More tellingly, Romney took only 18% of the vote among non-whites, but 32% of non-whites were for minor or no gun restrictions. This finding is confirmed in an April Pew poll. So, Democrats also have to reckon with a base that isn't as anti-gun as you might think.