Complex sentence: The longrifle developed on the American frontier in and about Lancaster, Pennsylvania in the 1740s, continued to be developed technically and artistically until it passed out of fashion in the second quarter of the 19th century.
Split into simpler sentences: The longrifle developed on the American frontier in and about Lancaster, Pennsylvania in the 1740s. It continued to be developed technically and artistically until it passed out of fashion in the second quarter of the 19th century.