All Rifle Calibers
Modern rifle ammo traces its roots back to France in the 1840's and the rimfire Flobert BB cap. This cartridge in .22 caliber was developed to be fired indoors, and was the cartridge on which all other rimfire rounds were based. Over the course of time, manufacturers adopted rimfire cartridges to be fired from rifles as small as .22 caliber to as large as .58 caliber. Shooters liked these rimfire cartridges right away because it made it faster and easier to reload their rifles than it was with a muzzle loader, and was easier to transport and store also.
Winchester introduced their .44 Winchester in 1873, which later came to be called the .44-40. The .44-40 was the first rifle cartridge to enjoy commercial success. Other companies soon after started to develop ammunition for their own rifles, and for being fired from their competitors' rifles as well. The .45 Colt and the .45-70 are two of the most famous rifle cartridges from 1873.
Smokeless powder was introduced just less than twenty years later, and the first cartridge which used smokeless powder to become commercially successful was the .30-30 Winchester, which was released in 1895. Slightly more than ten years later, the immensely popular .30-06 was released and then adopted by the US military. The .30-06 served in the military for over sixty years. Cartridge development was a booming business in the late 19th century and early 20th century, years that saw the introduction of smokeless powder and rimmed cartridges.
Cartridges and cases grew bigger and bigger until 1921, at which point we reached the pinnacle of rifle cartridges with the .50 Browning Machine Gun cartridge. The cartridge was of course not introduced for rifles, but the massive cartridge did punctuate the start of a trend toward smaller cartridges. This was mostly possible thanks to continuing advancements in powder and materials and bullet design.
The .270 Winchester, introduced in 1925, is a good example of a smaller cartridge. The .270 Winchester is a medium bore cartridge that continues to be among the most well-known and often-used rounds for hunting in North America. National militaries around the world also drove the development and advancement of rifle ammunition, especially during the 1940's, at which time the .30 Carbine and the 7.62x39mm appeared.
The 1950's and 1960's were great times for ammo innovation, especially for the Winchester company. Winchester released the .22 Winchester Magnum Rimfire, .243, .300 Winchester Magnum, .308, and .458 Winchster Magnum during these decades, and they have remained in great demand since.
The 1970's did not see much innovation for rifle ammunition. The 5.45x39mm was the most notable new cartridge of a limited bank of options. The 1980s and 1990's saw bore sizes growing and cartridge power increasing again with the 7mm-08 Remington and .338 Lapua leading the pack of the "bigger, faster, heavier" cartridges of the era.
Since the start of the new millennium, not many new cartridges have been released, and although some have been paraded with great fanfare, it is hard to speak of any real "game changers." If a shooter needed to select one great cartridge that they might expect to see still being produced in another fifty years, possibly the .300 AAC Blackout should be that cartridge.
As the old saying goes: "The more things change, the more they stay the same." Rifle ammo has changed immensely in the past century, but after all is said and done, it still just boils down to brass, powder, primer and bullet.