There was actually a study done on this by a Left wing writer for the publication, Mother Jones, who’s got no love for the Right...
His analysis actually found that, over the last 20 years, with regards to views on guns, taxes, abortion, etc, that the Right has, for the most part, stayed the same, or moved up to five percentage points to the Right...whereas the Left averaged a Leftward shift of 15-20 percentage points...yet the Left tries to make the Right out to be the extremists...