The .45-70 rifle cartridge, also known as .45-70 Government, was developed at the U.S. Army's Springfield Armory for use in the Springfield Model 1873 .45 caliber rifle, known to collectors (but never to the Army) as the "Trapdoor Springfield." The new cartridge was a replacement for the stop-gap .50-70 Government cartridge which had been adopted in 1866, one year after the end of the American Civil War.
The new cartridge was completely identified as the .45-70-405, but was also commonly called the ".45 Government" cartridge in commercial catalogs. The nomenclature of the time was based on several properties of the cartridge:
.45 : nominal caliber, in decimal inches i.e. 0.45 inches (11.4 mm)
70 : wt. of blackpowder charge, in grains i.e. 7000 grains 1 pound
405 : weight of lead bullet, 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 drop measured in 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 X 6 feet (1.8 m) at 600 yards (550 m) — the Army standard target, and a skill mainly of value 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 500-grain (32 g) bullet produced significantly superior ballistics, and could reach ranges of 3,500 yards (3200 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 roughly a 30 degree angle, penetrating 3 one 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 volleyed fire at ranges beyond those normally expected of infantry fire.
Note that while the nominal bullet diameter was .45 inches (11 mm), the bore was actually closer to .458 inches (11.6 mm). Arsenal loadings for the .45-70-405 and .45-70-500 government cartridges generally used bore diameter grease groove bullets of .457-.458 diameter. 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 are still available, and some black powder shooters still "roll their own" paper patched bullets for hunting and competitive shooting
The predecessor to the .45-70 was the short lived .50-70-425 cartridge, adopted in 1866 and used 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 bigger .50 caliber bullet 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 brass center-fire case design. A reduced power loading was also adopted for use in the Trapdoor carbine. This 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.
The 45 caliber rifle underwent a number of modifications over the years, the principal one being a strengthened breech starting in 1884. A new, 500 grain (32 g) bullet was adopted in that year for use in the stronger arm. The 45 caliber rifle was the principal arm of the US Army until 1893, long after European adoption of efficient repeaters using smokeless powder ammunition had made the American weapon obsolete as a military rifle. It was last used in quantity during the Spanish-American War, and was not completely purged from the inventory until well into the 20th century. Many surplus rifles were given to reservation Indians as subsistence hunting rifles and now carry Indian markings.
The .45-70 cartridge is still used by the U.S. military today, in the form of the CARTRIDGE, CALIBER .45, LINE THROWING, M32, a blank cartridge which is used in a number of models of line throwing guns used by the Navy 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.