Ron Guth:
The 1839-O Half Dime boasts a hefty mintage of over one million coins, yet among the early dates of this type, it remains a rarity in Mint State. According to the PCGS Population Report (as of December 2011), the 1839-O Half Dime is only slightly less common than the 1838-O and the 1840-O, both of which have lower mintages (substantially so in the case of the 1838-O) and only incrementally smaller mintages in Mint State.
Among the Mint State 1839-O Half Dimes, MS-63 is the median grade. In addition, PCGS has certified only four examples in MS-64, two in MS-65, and none finer.