Made Special for the RAF 303 Cartridges

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The .303" RAF special for aircraft was the same as regular .303" except made to tighter specs. The RAF special ammo can be distinguished by all four digits of the year in the hs vs two in other .303".
In the late 1930s it was decided to make all .303" to RAF standard and the the four digit date was dropped c1942.
Crimped primers were introduced c1916 with the introduction of the Hotchkiss LMG which had a tendency to blow primers.