In 1956 the Mint struck two different Types of Proof Franklin Half varieties. The 1956 Proof Type 1 lacked details on the eagles chest and the design shows four feathers on each side of the eagles' wings. The Mint then modified the reverse to a new Type 2 design. The 1956 Type 2 design will show three feathers on each side of the eagles' wings. The neck and feathers will also be much sharper compared to the Type 1.
The 1956 Type 2 reverse was used on most proof coins for that year. Therefore, the 1956 Type 1 is the most common variety from the two different reverses.