It has been far more difficult than I anticipated to outline this post in my mind. I will try to condense my thoughts without skipping any of the information I wanted to include.

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A Bit of History and Speculation

As I understand it, shotguns and rifles share a common history as shoulder-fired muskets were being developed in Europe. Early firearms all had smooth bore barrels, meaning they were no more than a tube. The theories I have read regarding the origin of rifles suggest that grooves were cut into the inside of barrels as a way to reduce fowling from black powder. This was called rifling. Some unnamed, unknown gunsmith, probably in Germany, added a spiral pattern to these grooves, and discovered the spiral rifling imparted a spin to the projectile and allowed far greater accuracy than smoothbore muskets could achieve.

These "rifled muskets" wouldn't become common military arms until the middle of the 19th century, right around the time of the American Civil War, but early colonists in America used them for hunting on the western frontiers of Appalachia, and militia riflemen used their far more accurate arms in combat to kill British officers from ambush in the Revolutionary War. This was seen as highly dishonorable by the proper military minds of the era, and George Washington preferred formations and continental-style combat despite the insanity of taking on what was arguably the best military of the era using the tactics they preferred.

Midern Rifle Development

Muskets used loose powder and lead balls or conical bullets as ammunition, and in later years, cartridges of premeasured powder and a bullet wrapped in paper became common. Following the US Civil War and the ongoing conflicts in Europe with Napoleon III, repeating rifles began to be used by various militaries as self-contained metallic cartridges were developed. In America, lever-action rifles had been developed prior to the Civil War, and the Henry carbine saw use among some volunteer units and state militias where it was allegedly known to Confederates as "That damned Yankee rifle you load on Sunday and shoot all week," but it would not be until well after the war that militaries began to seriously pursue repeating rifles for general issue.

In military arms, the bolt action pattern quickly became the favored design, culminating in the Mauser pattern and its derivatives that saw use through World War II, as well as several competing (or blatantly copied) designs. These are still popular hunting rifles, and as metallurgy, machining, and quality control have improved, they became the most accurate repeating rifle design available.

As the 20th century dawned, so did the semi-automatic rifle. The Remington Model 8 was, as far as I know, the first successful semi-automatic rifle designed for centerfire hunting caliber ammunition. Several semi-automatic rifles were fielded formally or informally in World War I, and by the time World War II rolled around, the semi-automatic Garand rifle was standard issue for US troops. Following World War II, semi-automatic and fully-automatic rifles and carbines became standard-issue for militaries around the world.

Carbines

A carbine is essentially a short, light rifle. In military contexts, sometimes it is a cut down version of a standard-issue rifle, and sometimes a special-purpose rifle firing a smaller cartridge. They were typically issued to cavalry, vehicle crews, and rear echelon troops where a full-length rifle would be more an impediment than a benefit.

In the civilian market, handy compact rifles are easier to carry in the field and easier to transport. They are often carried by campers, horseback riders, and hikers. Some, like the scout rifle, are purpose-built hunting tools that use full-power ammunition. Others are truck guns or boat guns carried in a vehicle where length is an undue encumbrance. Pistol-caliber carbines (PCC) are popular rifles for target shooting, pest control, and defense against man or beast. Many use the same magazines as popular semi-automatic pistols, and rifles that share their cartridges with revolvers have been popular at least since cowboy times.

Digressing slightly from the topic at hand, when the US military adopted the M16 rifle using its much lighter 5.56x45mm cartridge compared to the M14 with its 7.62x51mm cartridge, it was often perceived as a carbine itself. The m4 carbine is the short version of the M16.

The AR-15 rifle and shorter carbine-length variants are not identical to the M16 and M4 assault rifles, and should not be considered "assault weapons." I have covered that in depth previously, so I will limit my statement here to remind readers that the civilian models are just modern ergonomic rifles, and are not inherently more dangerous than any other small bore rifle or carbine. They are not "high-powered." The standard capacity magazines are 30 rounds. Don't panic. Lay off the legislative hype.

Other Rifles

This is by no means a comprehensive history of rifles or a complete catalog of designs. Pump-action hunting rifles are occasionally seen, and blowback .22LR rifles are perhaps the most common designs available. Single- and double-barrelled break-action rifles are still manufactured.Owners of modern incarnations and historical reproductions of the rifled musket are often granted special hunting seasons. Revolving rifles have been tried, but success has been limited due to the problem of hot gas and particulate matter blasting out from the cylinder gap between the chamber and the barrel.

Why a rifle?

Rifles are fired with the buttstock braced against the shooter's shoulder, the dominant hand operating the trigger, and the non-dominant hand supporting the forend. This makes a rifle much more stable than a pistol. When not equipped with a scope or other optic, a rifle also has a much greater distance between the front and rear sights, making it far easier to precisely align them with a target. As a general rule, all else being equal, a longer barrel means more power from a given cartridge since the expanding gas can propel the bullet to a far greater velocity, so even a PCC can improve the performance of the relatively low-powered pistol cartridges they fire.

Hunting rifles are commonly loaded with much higher-powered cartridges, capable of reliably stopping big game at very long range. "Varmint rifles" use lighter cartridges and are used for pest control, small game, or perhaps even deer-sized game, depending on the caliber and the hunter's marksmanship. The ubiquitous .22 LR is primarily used for target shooting and lower-cost marksmanship training, but it can also be used for small game, and I have heard rumors of people poaching deer with it.

The rifle is also a symbol of individual liberty. Rifles have been used by civilians to overthrow empires, to forge new lives in the wilderness, and to defend the home from hostile attacks. Today, a rifle may not be suitable against bombers, drones, and tanks, but those are still not the main tools of oppressive regimes. Police, soldiers, and politicians who intend to harm innocent people rightly fear the citizen rifleman. Meanwhile, hoplophobes demand more impositions upon us all in order to feel safe at the expense of our actual safety. This cannot be tolerated.

Hopefully this hasn't been to wordy or incoherent as I tried to condense a lot of information and my thoughts into a single post. Comments are welcome below. For more information, Wikipedia is probably a good starting point if you want to expand beyond this very brief overview of the topic. Ammo.com is also a good source of information online.