The new cartridge was completely identified as the .45-70-405, but was also referred to as the ".45 Government" cartridge in commercial catalogs. The nomenclature of the time was based on three properties of the cartridge:.45: nominal diameter of bullet, measured in decimal inches, i.e., 0.458 inches (11.63 mm);
70: weight of black powder, measured in grains, i.e., 70 grains (4.56 g);
405: weight of lead bullet, measured in grains, i.e., 405 grains (26.2 g).
The minimum acceptable accuracy of the .45-70 from the 1873 Springfield was approximately 4 inches (100 mm) at 100 yards (91 m), however, the heavy, slow-moving bullet had a "rainbow" trajectory, the bullet dropping multiple yards (meters) at ranges greater than a few hundred yards (meters). A skilled shooter, firing at known range, could consistently hit targets that were 6 × 6 feet (1.8 m) at 600 yards (550 m)—the army's standard target. It was a skill valuable mainly in mass or volley fire, since accurate aimed fire on a man-sized target was effective only to about 300 yards (270 m).
After the Sandy Hook tests of 1879, a new variation of the .45-70 cartridge was produced: the .45-70-500, which fired a heavier, 500 grain, (32.5 g) bullet. The heavier bullet produced significantly superior ballistics, and could reach ranges of 3,350 yards (3,120 m), which were beyond the maximum range of the .45-70-405. While the effective range of the .45-70 on individual targets was limited to about 1,000 yards (915 m) with either load, the heavier bullet would produce lethal injuries at 3,500 yards (3,200 m). At those ranges, the bullets struck point-first at a roughly 30 degree angle, penetrating three 1-inch (2.5 cm) thick oak boards, and then traveling to a depth of 8 inches (20 cm) into the sand of the Sandy Hook beach. It was hoped the longer range of the .45-70-500 would allow effective volley fire at ranges beyond those normally expected of infantry fire.
While the nominal bore diameter was .450 inches (11.4 mm), the groove diameter was actually closer to .458 inches (11.6 mm). As was standard practice with many early U.S. commercially produced cartridges, specially-constructed bullets were often "paper patched", or wrapped in a couple of layers of thin paper. This patch served to seal the bore and keep the soft lead bullet from coming in contact with the bore, preventing leading (see internal ballistics). Like the cloth or paper patch used in muzzleloading firearms, the paper patch fell off soon after the bullet left the bore. Paper-patched bullets were made of soft lead .450 inches (11.4 mm) in diameter. When wrapped in two layers of thin cotton paper, this produced a final size of .458 inches (11.6 mm) to match the bore. Paper patched bullets are still available, and some black-powder shooters still "roll their own" paper patched bullets for hunting and competitive shooting. Arsenal loadings for the .45-70-405 and .45-70-500 government cartridges generally used groove diameter grease groove bullets of .458 inches (11.6 mm) diameter.
The predecessor to the .45-70 was the .50-70-450 cartridge, adopted in 1866 and used until 1873 in a variety of rifles, many of them percussion rifled muskets converted to trapdoor action breechloaders. The conversion consisted of milling out the rear of the barrel for the tilting breechblock, and placing a .50 caliber "liner" barrel inside the .58 caliber barrel. The .50-70 was popular among hunters, as the bullet was larger than the .44 caliber and also hit harder (see terminal ballistics), but the military decided even as early as 1866 that a .45 caliber bullet would provide increased range, penetration, and accuracy. The .50-70 was nevertheless adopted as a temporary solution until a significantly improved rifle and cartridge could be developed.
The result of the quest for a more accurate, flatter shooting, .45 caliber cartridge and firearm was the Springfield trapdoor rifle. Like the .50-70 before it, the .45-70 used a copper center-fire case design. A reduced power loading was also adopted for use in the trapdoor carbine. It had a 55 grain (3.6 g) powder charge.
Also issued was the .45-70 "forager" round, which contained a thin wooden bullet filled with birdshot, intended for use hunting small game to supplement the soldiers' rations. This round in effect made the .45-70 rifle into a 49 gauge shotgun (or more accurately, a .410 shotgun, as the .410 shell is the same diameter as a .45 Colt, another straight-walled, .45 caliber cartridge).
The .45-caliber Springfield underwent a number of modifications over the years. The principal modification was a strengthened breech starting in 1884. A new, 500 grain (32 g) bullet was adopted in that year for use in the stronger receiver breech. The M1873 and M1884 Springfield rifles were the principle small arms of the US Army until 1893.
The .45-70 round was also used in several Gatling gun models from 1873 until being superseded by the .30 Army round beginning with the M1893 Gatling gun. Some .45-70 Gatling guns were used on US Navy warships launched in the 1880s and 1890s.
The US Navy used the .45-70 caliber in several rifles: the M1873 and M1884 Springfield, the Model 1879 Lee Magazine Navy Contract Rifle, and the Remington–Lee, the last two being magazine-fed turnbolt repeating rifles. The US Marines used the M1873 and M1884 Springfield in .45-70 until 1897, when supplies of the new M1895 Lee Navy rifle in 6mm Lee Navy, adopted two years before by the US Navy, were finally available.
Realizing that single-shot black-powder rifles were rapidly becoming obsolete, the US Army adopted the Norwegian-designed .30 Army caliber as the Springfield Model 1892 in 1893. However, the .45-70 continued in service with National Guard, the Navy, and the Marines until 1897. The .45-70 was last used in quantity during the Spanish–American War, but was not completely purged from inventory until well into the 20th century. Many surplus rifles were also given to reservation Indians for use as subsistence hunting rifles and now carry Indian markings.
The .45-70 cartridge is still used by the U.S. military today (2017), in the form of the "cartridge, caliber .45, line throwing, M32" blank cartridge which is used in a number of models of line throwing guns used by the Army and Coast Guard. Early models of these line throwing guns were made from modified trapdoor and Sharps rifles, while later models are built on break-open single-shot rifle actions.
As is usual with military ammunition, the .45-70 was an immediate hit among sportsmen, and the .45-70 has survived to the present day. Today, the traditional 405-grain (26.2 g) load is considered adequate for any North American big game within its range limitations, including the great bears, and it does not destroy edible meat on smaller animals such as deer due to the bullet's low velocity. It is very good for big-game hunting in brush or heavy timber where the range is usually short. The .45-70, when loaded with the proper bullets at appropriate velocities, has been used to hunt the African "big-six". The .45-70 has been loaded and used to harvest everything from birds to elephant and the cartridge is still undergoing new development work well over a century after its introduction.
The trajectory of the bullets is very steep, which makes for a very short point-blank range. This was not a significant problem at the time of introduction, as the .45-70 was a fairly flat-shooting cartridge for its time. Shooters of these early cartridges had to be keen judges of distance, wind and trajectory to make long shots; the Sharps Rifle in larger calibers such as .50-110 was used at ranges of 1,000 yards (910 m). Most modern shooters use much higher velocity cartridges, relying on the long point-blank range, and rarely using telescopic sights' elevation adjustments, calibrated iron sights, or hold-over. Sights found on early cartridge hunting rifles were quite sophisticated, with a long sighting radius, wide range of elevation, and vernier adjustments to allow precise calibration of the sights for a given range. Even the military "creedmoor" type rifle sights were calibrated and designed to handle extended ranges, flipping up to provide several degrees of elevation adjustment if needed. The .45-70 is a popular choice for black-powder cartridge shooting events, and replicas of most of the early rifles, including trapdoor, Sharps, and Remington single-shot rifles, are available.
The .45-70 is a long-range caliber but it takes adequate knowledge of windage and elevation. The .45-70 retains great popularity among American hunters for the niche it is suited for, and is still offered by several commercial ammunition manufacturers. Even when loaded with modern smokeless powders, pressures are usually kept low for safety in antique rifles and their replicas. Various modern sporting rifles are chambered for the .45-70, and some of these benefit from judicious handloading of home-made ammunition with markedly higher pressure and ballistic performance. Others, which reproduce the original designs take the original load, but are not strong enough for anything with higher pressure. In a rifle such as the Siamese Mauser (commonly converted to fire .45-70 due to it being the only Mauser 98 derivative designed to feed rimmed cartridges, and the limited availability of ammunition for its original 8×50mmR chambering) or a Ruger No. 1 single-shot rifle, can be handloaded to deliver good performance even on big African game. The .45-70 has also been used in double rifles since the development of the Colt 1878 rifle and the more modern replicas, like the Kodiak Mark IV.
In addition to its traditional use in rifles, Thompson Center Arms has offered a .45-70 barrel in both pistol and rifle lengths for their Contender single-shot pistol, arguably the most potent caliber offered in the Contender frame. Even the shortest barrel, 14 inches, is easily capable of producing well over 2,000 ft·lbf (2,700 J) of energy, double the power of most .44 Magnum loadings, and a Taylor KO factor as high as 40 with some loads. Recent .45-70 barrels are available with efficient muzzle brakes that significantly reduce the muzzle rise and also help attenuate the recoil. The Magnum Research BFR is a heavier gun at approximately 4.5 pounds, helping it have much more manageable recoil.
Only with the recent introduction of ultra-magnum revolver cartridges such as the .500 S&W Magnum have production handguns begun to eclipse the .45-70 Contender in the rarefied field of big-game-capable handguns.