Original sentence: The first MP5 models used a double-column straight box magazine, but since 1977, slightly curved, steel magazines are used with a 30-round capacity (weighing 0.12 kg) or a 30-round capacity (0.17 kg empty)
Edited sentence: The first MP5 models used a double-column straight box magazine, but since 1977, slightly curved, steel magazines are used with a 15-round capacity (weighing 0.12 kg) or a 30-round capacity (0.17 kg empty)