Complex sentence: The fourth generation of the CZ 99 family is the Zastava CZ-05 which entered mass production in spring of 2007, which is essentially a CZ 999 pistol with an underbarrel picatinny rail attached to it.
Split into simpler sentences: The fourth generation of the CZ 99 family is the Zastava CZ-05, which entered mass production in spring of 2007. This is essentially a CZ 999 pistol with an underbarrel picatinny rail attached to it.