Ron Guth:
1863 saw a precipitous decline in the mintage of the Quarter Dollars, signalling the start of a more gradual drop-off that lasted for the next decade. In fact, the next time that a mintage would exceed that of the 1863 was in 1873, when a change in the weight of the silver coins forced a renewed effort to make replacement Quarters for those removed from circulation.
Even with its reduced mintage, the 1863 is not a particularly rare coin. Several dozen Mint State examples are known, ranging in grades from MS61 to MS66, with most examples appearing in MS64 and MS65. The finest example is a single MS66+.