It was first discovered in Europe during the Early Modern Era that internally grooved or rifled barrels could provide better accurracy to shot being fired out of them. Although this principle was known to most civilisations, rifled barrels weren't very practical for one reason: the propellant of the day, gunpowder or black powder, did not always burn away, meaning that rifles were hard to clean. To make matters worse, black powder itself was corrosive, so rifled barrels were more of an exception than the rule.