Complex sentence: The open bolt design exposes the breech end of the barrel, and improves cooling during periods of continuous fire; however, it means that since the bolt is held to the rear when cocked, the receiver is more susceptible to contamination from sand and dirt ingress.
Split into simpler sentences: The open bolt design exposes the breech end of the barrel, and improves cooling during periods of continuous fire. However, it means that since the bolt is held to the rear when cocked, the receiver is more susceptible to contamination from sand and dirt ingress.