Unit Information Game Strategies History
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.

Rifles were indeed accurate but were very slow to reload since the use of black powder necessitated cleaning after each shot, so as a result, rifled guns were mostly highly experimental weapons which were seldom used on the field. Only when nitroglycerine and smokeless powders, along with expanding-base bullets were introduced in the 1850s did firearms with rifled barrels began to be adopted on a widespread basis.

The first rifle meant for mass use was the Baker rifle, first invented by Ezekiel Baker. Highly accurate, it was however costly to create (owing to the rifling process) and difficult to maintain, so it was issued solely to British elite skirmishers. Nevertheless, it still outperformed the "Brown Bess" muskets and by the 1840s had mostly displaced muskets in the British Army, and even played a major part in wars in Mexico and Latin America. For this reason, rifles still had to wait a little longer to gain popularity until the introduction of the Minié system by a French army captain that rifles began to take off and become more popular. Claude-Étienne Minié's system involved replacing musket balls, which were mostly spherical and made of lead, with a cone-shaped expanding-base bullet. This meant that the bullet was harder, yet could easily come in contact with the grooves of the rifle barrel for greater accuracy. 

Even so, these two discoveries - grooved barrels and expanding-base ammunition - did not generally create a change in tactics until the emergence of breech-loading systems to replace the earlier muzzle-loading rifles and muskets, drastically increasing the rate of fire (as well as the range) of guns. New breech-loading mechanisms, developed independently of each other in Europe, soon meant that modern infantry armed with these weapons would have a marked edge over those still using more primitive musketry. Equally, they also carried bullets with a higher calibre that could shatter bone on impact owing to their immense velocity, resulting in the first few chapters of the history of industrial warfare being marked by mass casualties whenever armies clashed owing to the new destructive power of modern combat rifles.

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