More or less ubiquitous in combat and historical reenactment, the rifle is a proud member of the pantheon of great inventions. The child of the blackpowder musket, which was the child of the Arquebus, which was the child of exploding gunpowder in large heavy pots with projectiles wedged in them, the rifle changed military combat worldwide.
Named for the swirling grooves on the inside of the barrel, rifles (technically called “rifled guns” in a flash of name dropping genius) revolutionized the world of armed conflict by allowing footsoldiers effective range that rivaled early artillery. Where cannons could once fire repeatedly upon soldiers with grape shot and no fear of returned fire, artillery crews found themselves within the max range of the new guns. This forced cannon crews to rely more heavily on longer range and less effective rounds, improving the effectiveness of infantry to a great degree.
Scientifically, the rifle was a monumental creation because it finally broke free from the confines of musket range, but only when it worked in tandem with another great invention (one that gets way less of the fame). Muskets would blast a small spherical ball of lead towards their target, which worked great until around 300 yards. After 300 yards, the aim was nonexistent and the likelihood of hitting a target was low. Gunsmiths knew that having rifling in the barrel would theoretically improve the range and accuracy of the gun, but the rifling on the tube would allow too much of the explosion to eek around the round and would dramatically reduce the range and stopping power of the gun. Gunsmiths assumed that you would need a perfectly sized bullet, form fit to the individual quirks and shapes of each rifle, and essentially said that a rifled gun would never fire as well as a musket would because bullets made for a gun with rifling could never be perfect for each rifle and produced in mass quantities.
It wasn’t until Claude Minie invented his own bullet that rifles began to be used. His invention was a small conical round (the kind that were used in the American Civil War) with a ring of soft lead around the base (best descriptions can be found on Wikipedia’s minie ball link). The ring of soft lead would be wedged into the barrel and when the gunpowder would go off, the ring would get blasted outward and would form a seal around the rifling, bypassing the issue that people had with rifling. With bullets that would then form fit themselves to the barrel of any rifle, the gun began to become more popular and the days of the musket and smoothbore barrels began to rapidly close.
Minie’s bullets only lasted for a short time though. Within a century of his creation, breechloading rifles and the creation of what would be known as cartridge rounds quickly outstripped his bullet in the speed they could be loaded and fired. Minie was the one who put the rifle on the radar, but it was the creation of repeaters and Colt and Springfield who pressed the guns to the fame they hold today.
Hessian Riflemen (http://flintlockandtomahawk.blogspot.com/2011_09_01_archive.html)