Complex sentence: These "rifled muskets" or "rifle muskets" were long enough to serve the function of muskets in close formations of line and square, were as quick to load as the old muskets and as easy to use with a minimum of training.
Split into simpler sentences: These "rifled muskets" or "rifle muskets" combined the advantages of rifles and muskets. They were long enough to serve the function of muskets in close formations of line and square, they were as quick to load as the old muskets and as easy to use with a minimum of training.