Stevo is correct. The "43" refers to the Soviet designation M43, abbreviated from the year the cartridge was developed - 1943. It also generally denotes a specific bullet type and construction as the 7.62x39 load most are familiar with (lead 123gr spitzer) is in fact a Yugoslav design known as the M67. The M43 is a steel core boat tail. It can definitely be confusing given the various suffixes of 7.62mm to come out of the Soviet bloc; 7.62x25, 7.62x39, 7.62x45, 7.62x54R...
The number 43, however, will always reference type M43 ball.
Additionally, as mentioned above look more closely at the markings on the crate and you will notice it is not 7.62 x 43 but 7.62 - 43.