5.56 History 01: Rifle Caliber and Muzzle Velocity Trends

This is the first post in a planned series on the evolution of the 5.56 NATO round, and served to put the round in its context in the ongoing flow of small-arms history.

The long-term trend in small arms design has been to higher velocities and smaller calibers. Everybody knows that, but here it is in tables and pictures. Beginning in 1775, with the seminal battles of Lexington and Concord on April 18, here’s the caliber and muzzle velocity of the main US infantry weapon, sampled at 25-year intervals, to 2000.








Long Land Pattern Flintlock Musket (Brown Bess)




US M1795 flintlock musket




US M1816 flintlock musket




US M1841 percussion “Mississippi” Rifle




US M1873 “trapdoor” Springfield




M1898 .30-40 Krag




M1903 .30-06 Springfield M1 ball




M1 .30-06 Garand M2 ball




M16A1 5.56 M193




M16A2 5.56 M855

One can quibble with these velocities, especially for the older muzzle-loaders, where the individual operator has more influence on velocity than he would after the invention of fixed ammunition. You notice a couple of burbles in the velocity trend. The first came when the Army committed to rifled weapons, which steal some velocity vis-a-vis smoothbores, but deliver much greater accuracy. The second came when the heavier M855 projectile replaced the lighter M193, in pursuit of greater penetration downrange. As a rule of thumb, the lighter projectile, the faster.

The two things driving this history of improvement have been:

1. Competition between the world’s armies, which ensures that any real improvement that conveys a military advantages is spread worldwide as quickly as military budgets allow, and:

2. Smaller calibers and higher velocities have been enabled by improvements in propellant chemistry, metallurgy, and manufacturing.

In addition, weapons concepts and pure research have occasionally driven developments; but the constraints limiting progress are the budgets which means that any advance must truly confer an advantage, and the technology which means the advance must be able to be made within the state of the art.

1775: .69 to .75 caliber flintlock muskets

The Revolutionary War was fought with smoothbore flintlock muskets. The standard British weapon was the .75 Caliber Long Land Pattern Musket, aka “Brown Bess.” The analogous French musket, the .69 inch Charleville,  The same technology equipped military weapons until the obvious advantages of percussion replaced the flintlock over a long period from about 1830 to 1845. Those advantages included more reliable ignition, faster reloading, better weather proofing and even a little more velocity due to the closed touchhole.

1860: .58 caliber Springfield rifled musket

By the outbreak of the Civil War, the musket’s caliber was a little smaller, and more importantly, the standard issue weapon had a rifled bore. In 1860 there were still many stands of old smoothbores that had been converted to percussion, but since 1841 the US military had been willingly taking a velocity hit for the higher accuracy of a tight-fitting Minié ball in a rifled bore.

1880: .45 caliber “trapdoor” Springfield Rifle

As the Civil War raged, metallic fixed ammunition and breech loading advanced, and after the war the US began to convert its mountains of muskets to breech-loading (other nations, as always, were carrying out parallel developments, like the British Snyder). In a few short years rifle caliber dropped to .50, then to the .45-70 with which Custer faced Sitting Bull.

1900: .30 caliber M1898 Krag bolt-action rifle

The US entered the Spanish-American War of 1898 proud and confident in its new .30-40 Krag rifle, a smooth repeater firing a modern, albeit rimmed, smokeless-powder cartridge. But they discovered that the Spaniards had, if less luck on the battlefield, a much better gun, the 7 x 57 mm Mauser. The US licensed Mauser’s design and fought a World War with it, using an extended .30 caliber cartridge (in metric terms, 7.62 x 63mm). The cartridge soldiered on through the Korean War in the M1 Garand, and even served until 1970 as the principal rifle of the South Vietnamese Army.

The Garand’s replacement was… well, really, the Garand. The M14 had an improved gas syatem, a box magazine, and an effective flash hider, but it was pretty much a Garand. The human engineering was done pretty well: most shooters who’ve handled both think the M14 is more compact, when actually it’s longer and has the protruding magazine. The 7.62mm NATO round used in the M14 was designed t0 take advantage of new powder technology and provide the same ballistics as the old M2 Ball round used in the M1.

1963: .223 caliber (5.56mm) M16 Rifle

The next quantum leap came with the 5.56 round, which we’re going to be covering a lot here on WeaponsMan.com. The initial impetus came from a 1930 Aberdeen Proving Ground study on the potential of a Small Caliber High Velocity weapon and ammunition. The author theorized that the bullet could be made stable in air, but unstable in a denser medium like human flesh. Meanwhile, many gunsmiths were developing high velocity rounds for sporting purposes, often by taking a larger cartridge and necking the case down to approximately .22 inch.

The military conducted some desultory experiments with small caliber weapons, but was blindsided by an Air Force request for an off-the-shelf buy of a commercially-developed light rifle, the AR-15. Armalite, the makers of the AR-15, had developed a weapon and round together, using aerospace technologies to make the rifle light, compact, and ergonomic. Soon, Army Ordnance found itself force-fed the M16 by the “whiz kids” in Robert S. Macnamara’s Department of Defense.

Most of Macnamara’s initiatives, whether to make the Air Force and Navy share the same airplane for different missions, or to see what would happen if you jammed 100,000 borderline-retarded recruits into the Army and Marines, ranged from failure to catastrophe. But the M16 has overcome much adversity and escaped the Curse of Macnamara: despite him, it works.

Tune in from time to time for further installments of 5.56 — and of course, M16 – history.