Complex sentence: The caseless ammunition large-caliber rounds were themselves troublesome because the casings did not burn completely, requiring a complicated and slow gas-driven scavenging system, and they were liable to cook off if the vehicle were hit.
Split into simpler sentences: The caseless ammunition large-caliber rounds were themselves troublesome because the casings did not burn completely, requiring a complicated and slow gas-driven scavenging system. They were also liable to cook off if the vehicle were hit.