Complex sentence: The cartridge was originally marked with six cannelures in the middle, but this weakened the case and caused it to burst in a dirty rifle; it was late marked by six dents or flutes on the shoulder of the cartridge.
Split into simpler sentences: The cartridge was originally marked with six cannelures in the middle, but this weakened the case and caused it to burst in a dirty rifle. It was later marked by six dents or flutes on the shoulder of the cartridge.