Complex sentence: The gun used 250-round fabric belts of 7.92 × 57mm ammunition, although sustained firing would lead to overheating; it was water-cooled, using a jacket around the barrel that held approximately one gallon of water.
Split into simpler sentences: The gun used 250-round fabric belts of 7.92 × 57mm ammunition. It was water-cooled, using a jacket around the barrel that held approximately one gallon of water.