This is the last year in which Franklin Half Dollars were struck. The 1963-D Franklin Half Dollar also happens to have the largest mintage in the entire series. The Mint struck over 65 million of them for this issue, compare this to the mintage of the1955-P where just under 2.5 million were struck.
Therefore the 1963-D is very common in circulated grades up to MS64 condition they can still be bought in rolls. In MS65 condition many of them are sold as singles and in MS66 condition command a significant premium with many of them already being graded. There are no MS67 examples known, more than likely the large amount of coins produced affected the quality as the Denver Mint was not use to producing this many Half Dollars in a single year and quality was probably not their primary concern.