Ron Guth: The Act of May 16, 1866 authorized a new five cent coin made of 25% nickel and 75% copper. This created the unusual situation where two coins of the same value circulated simultaneously (the other coin being the Half Dime). A massive quantity of nearly 15 million new "Nickels" was produced in the first year, partly to promote the new coin and partly because of the availability of nickel and copper compared to the higher cost of silver for Half Dimes. The first versions of the new Nickel included rays on the reverse, between the stars surrounding the large 5 at the center of the coin. These extra elements caused the coinage dies to fail early because of the extra pressure needed to strike the nickel alloy and to force the metal into the recesses of the dies. To correct this problem, mint officials ordered the removal of the rays in mid-1867, creating two varieties: With Rays and No Rays. Striking problems persisted, resulting in a series of coins noted for inconsistent strikes and lots of die cracks.
None of the dates in the Shield Nickel series is particularly rare, although the Proof-only 1877 and 1878 can be elusive and command a nice premium. The low mintage 1880 Nickel is always a favorite with collectors, no matter the grade.
Proofs of most dates are readilyavailable, but the 1867 With Rays Proof is excessively rare. Oftentimes, discerning between prooflike circulation strikes and true proofs can be problematic, particularly with the dates in the late 1870s and those from the 1880s.
Interesting varieties include a widely repunched date in 1866, the Open and Close 3's of 1873, 1879/8, and 1883/2.