A standard 5.56×45mm NATO round leaves the muzzle of a full-length rifle barrel at roughly 3,000 to 3,250 feet per second, depending on the specific load and barrel length. That translates to about 2,000 to 2,200 miles per hour, or roughly three times the speed of sound. The number varies more than most people expect, though, because barrel length, bullet weight, propellant charge, ambient temperature, and even barrel condition all shift the result by meaningful amounts.
The Baseline Numbers
The 5.56×45mm NATO cartridge was originally designed around a 20-inch barrel, the length used on the M16 rifle. From that barrel, the two most commonly referenced military loads produce distinctly different speeds. The older M193 round, loaded with a 55-grain bullet, typically clocks around 3,240 feet per second. The newer M855 “green tip” round, loaded with a heavier 62-grain bullet, runs closer to 3,020 feet per second from the same barrel. Both figures come from standard test conditions at sea level and moderate temperatures.
Commercial 5.56 and .223 Remington ammunition spans an even wider range. Light varmint loads pushing 40- or 45-grain bullets can exceed 3,600 feet per second, while heavy 77-grain match rounds like the Mk 262 settle around 2,750 feet per second. The cartridge’s versatility is part of why it dominates both military and civilian use, but it also means that quoting a single “5.56 muzzle velocity” without specifying the load and barrel is a bit like quoting a car’s top speed without naming the model.
Why Barrel Length Changes Everything
The propellant inside a 5.56 cartridge generates a cloud of expanding gas that pushes the bullet forward for as long as the bullet remains inside the barrel. A longer barrel gives the gas more time to accelerate the projectile before it exits. Once the bullet clears the muzzle, that acceleration stops instantly and drag begins slowing it down. This is why barrel length is probably the single biggest variable in muzzle velocity for any given load.
The original M16’s 20-inch barrel extracts close to the full potential of the cartridge. When the U.S. military transitioned to the M4 carbine with its 14.5-inch barrel, the same M855 ammunition dropped to roughly 2,900 feet per second, a loss of around 100 to 120 feet per second. That might sound modest, but velocity losses are not linear with barrel length. Chopping additional inches costs disproportionately more speed. An AR-platform pistol or short-barreled rifle with a 10.3-inch barrel firing the same round often reads around 2,500 to 2,600 feet per second on a chronograph, losing 400-plus feet per second compared to the full-length setup.
Researchers studying NATO-standard 5.56mm barrels have modeled how projectile velocity builds as a function of travel distance inside the bore, confirming that the relationship between barrel position and velocity follows a predictable curve that flattens as the bullet approaches the muzzle.1Measurement. Semi-empirical prediction of internal pressure distribution and muzzle velocity in the rifled barrel of a light weapon In plain terms, the first few inches of barrel do the most work, and each additional inch contributes a bit less. By the time you reach 20 inches, you are getting diminishing returns, which is why military rifles rarely go longer and why bull-barrel target setups at 24 inches only add another 50 to 80 feet per second beyond the 20-inch baseline.
For the reader trying to estimate velocity from a specific barrel, a rough rule of thumb for 5.56 loads is that you lose about 25 to 30 feet per second per inch of barrel removed below 20 inches. That estimate gets less reliable below about 12 inches, where losses per inch can be steeper.
How Bullet Weight Trades Off Against Speed
Within the same cartridge case, heavier bullets leave the muzzle slower and lighter bullets leave faster. The amount of propellant is roughly the same in most factory loads (typically 25 to 28 grains of powder), so the total energy available is similar. A lighter projectile accelerates more easily, reaching higher peak velocity, while a heavier one requires more push to get moving.
The practical range of bullet weights in 5.56/.223 runs from about 35 grains at the ultralight end up to 90 grains for specialized subsonic loads. The most common weights cluster between 55 and 77 grains. Here is a rough picture of what those different weights look like from a 20-inch barrel:
- 40-grain varmint: Around 3,600 to 3,700 feet per second. Extremely fast, but sheds velocity quickly due to a less aerodynamic shape.
- 55-grain M193: Around 3,240 feet per second. The classic lightweight military load.
- 62-grain M855: Around 3,020 feet per second. The standard NATO ball round.
- 77-grain Mk 262: Around 2,750 feet per second. A match-grade load favored for precision at longer range.
The heavier bullets, despite starting slower, often retain their velocity better at distance because they have higher ballistic coefficients, meaning they slip through the air more efficiently. A 77-grain Sierra MatchKing bullet might leave the muzzle 500 feet per second slower than a 55-grain M193, but by 400 or 500 yards the gap narrows considerably. This tradeoff between launch speed and downrange retention is a central consideration for anyone choosing a load for a specific purpose.
What Happens to Velocity After the Bullet Leaves the Barrel
Muzzle velocity is the peak. From the instant the bullet exits, aerodynamic drag begins eating away at its speed. How fast that decay happens depends on the bullet’s shape, weight, and the density of the air it is flying through.
A typical 62-grain M855 round fired at 3,020 feet per second from a 20-inch barrel will slow to roughly 2,500 feet per second at 200 yards and around 2,000 feet per second at 400 yards. By 600 yards, it is down to approximately 1,500 feet per second. At some point between 600 and 800 yards, depending on conditions, the bullet drops through the transonic zone, where its speed transitions from supersonic to subsonic. That transition, around 1,125 feet per second at sea level, is aerodynamically turbulent and tends to destabilize the bullet, making accuracy unpredictable beyond that range.
This velocity decay matters because the 5.56 round relies heavily on speed for its terminal effectiveness. Unlike larger, heavier rifle cartridges that carry substantial momentum at lower velocities, the 5.56 is a small, light projectile that depends on high impact velocity to fragment or yaw inside a target. Many ballistics experts cite a threshold of around 2,500 feet per second as the point below which M855 and M193 bullets become much less likely to fragment reliably. From a 14.5-inch M4 barrel, that threshold is crossed at a shorter range than from a 20-inch barrel, which is one reason the military’s shift to shorter barrels generated decades of debate about the round’s effectiveness.
Temperature, Altitude, and Other Environmental Variables
Propellant is a chemical compound, and like all chemical reactions, its burn rate is sensitive to temperature. A cartridge that has been sitting in a hot vehicle on a 110°F day will generate higher chamber pressure and push the bullet faster than the same cartridge fired in sub-zero conditions. The U.S. military has studied this effect specifically for small arms ammunition, documenting that propellant temperature meaningfully shifts muzzle velocity.2Defense Technical Information Center. Change in Muzzle Velocity due to a Change in Propellant Temperature for Small Arms Ammunition
As a general guideline, shooters can expect velocity to change by roughly 1 to 2 feet per second per degree Fahrenheit of propellant temperature change, though the exact sensitivity depends on the specific powder used. Over the range of temperatures a shooter might encounter in the field, from well below freezing to desert heat, that can add up to 100 feet per second or more of variation. This is one reason military and competitive shooters track ambient temperature and adjust their ballistic calculations accordingly.
Altitude also plays a role, though it affects the bullet’s flight rather than its launch speed. At higher elevations, the air is thinner, which means less drag. A bullet fired at 7,000 feet above sea level retains its velocity longer than the same bullet fired at sea level. The muzzle velocity itself does not change (the propellant burns inside the sealed chamber regardless of outside air pressure), but the effective range stretches because the bullet decelerates more slowly in thinner air.
Humidity has a counterintuitive effect. Moist air is actually slightly less dense than dry air at the same temperature and pressure, because water molecules are lighter than the nitrogen and oxygen molecules they displace. In practice, the difference is small enough that most shooters can ignore it, but precision competitors at very long range sometimes account for it.
Barrel Wear and Velocity Loss Over Time
A rifle barrel is not a permanent component. Every round fired sends a jet of superheated gas and a copper-jacketed bullet scraping down the bore at enormous pressure. Over thousands of rounds, this erodes the barrel, particularly at the throat, which is the section just forward of the chamber where the bullet first engages the rifling. As the throat erodes, the bullet gets a looser start, gas seeps past it more easily, and peak pressure drops. The result is a gradual decline in muzzle velocity.
Research into barrel erosion has quantified some of these changes in measurable terms. One study found that by the end of a barrel’s useful life, the resistance the rifling exerts on the bullet’s rotating band drops by roughly 39%, and the surface contact force between the bullet and the rifling lands drops by about 36%.3Journal of Physics: Conference Series. Erosion and wear of barrel and its impact on projectile force At the same time, the impact force between the bullet’s bearing surface and the barrel increases substantially due to changed geometry, which contributes to further wear. In practical terms, a well-used 5.56 barrel can lose 50 to 100 feet per second compared to its original performance before accuracy degrades enough for the shooter to notice a problem.
The typical service life of a quality 5.56 barrel is often quoted at 10,000 to 20,000 rounds, though this varies enormously with firing schedule, barrel material, and how hot the barrel gets during use. Chrome-lined barrels, standard on most military rifles, resist erosion better than unlined stainless steel match barrels but may sacrifice a small amount of peak accuracy. Rapid sustained fire accelerates wear dramatically because it keeps the barrel at higher temperatures, which softens the steel and increases erosion per shot.
Putting the Speed in Context
Numbers like 3,000 feet per second are hard to grasp intuitively. Some comparisons help. The speed of sound at sea level is roughly 1,125 feet per second, so a 5.56 bullet at 3,000 feet per second is traveling at about Mach 2.7. A commercial jet cruises at about 550 to 600 miles per hour; a 5.56 bullet at the muzzle is moving at about 2,100 miles per hour, roughly three and a half times faster than the plane. A pitched baseball tops out around 100 miles per hour. The bullet is roughly 20 times faster.
At 3,000 feet per second, the bullet covers the length of a football field in about a tenth of a second. At 500 yards, the time of flight is closer to three-quarters of a second, because drag is slowing the bullet continuously. This is fast enough that at typical engagement distances for the round, say out to 300 yards, the bullet arrives before the sound of the shot does. A person 200 yards away would be struck roughly 0.2 seconds after the trigger breaks; the sound would not arrive for another 0.3 to 0.4 seconds after that.
5.56 NATO Versus .223 Remington
These two cartridges are dimensionally identical and often used interchangeably, but they are not quite the same. The 5.56 NATO specification allows for higher chamber pressure than commercial .223 Remington. NATO-spec ammunition is loaded to produce higher velocities, and the chamber dimensions of a 5.56 NATO barrel include a slightly longer throat (called the “leade”) to accommodate those pressures safely.
In practice, the velocity difference between the two is modest, often 50 to 100 feet per second for similar bullet weights, with the 5.56 NATO load running hotter. The safety concern runs in one direction: firing 5.56 NATO ammunition in a rifle chambered exclusively for .223 Remington can produce pressures above what the chamber was designed for, because the shorter throat of the .223 chamber causes the bullet to engage the rifling sooner, spiking pressure. Most modern AR-platform rifles are chambered for 5.56 NATO or the hybrid “.223 Wylde” chamber, which handles both safely. But bolt-action rifles and older platforms marked “.223 Remington” only should stick with .223-pressure ammunition.
Why the Military Keeps Chasing More Speed
The U.S. Army’s Next Generation Squad Weapon program, which fielded the XM7 rifle and its 6.8×51mm cartridge beginning in 2022, was driven partly by a desire for higher muzzle velocity and better downrange performance than the 5.56 can deliver from shorter barrels. The 6.8×51mm operates at substantially higher chamber pressures than 5.56 NATO and pushes a heavier bullet at comparable or higher velocities, aiming to defeat modern body armor at distances where the 5.56 has lost too much energy.
This does not mean the 5.56 is going away. It remains the standard NATO cartridge for most allied forces, and its combination of low recoil, light weight (roughly half the weight per round compared to 7.62 NATO), and adequate terminal performance at moderate range makes it hard to replace entirely. A soldier carrying 210 rounds of 5.56 can carry the same weight as about 100 rounds of 7.62 NATO, and that logistical advantage matters enormously in sustained operations. The 5.56’s velocity, even from shorter barrels, remains high enough to be effective within the ranges where most infantry engagements actually happen, which multiple studies over decades have consistently placed at under 300 meters.
Suppressor Effects on Velocity
A common misconception is that attaching a suppressor to a rifle reduces the bullet’s velocity. In reality, suppressors tend to increase muzzle velocity slightly, typically by 10 to 40 feet per second with 5.56 ammunition. The reason is straightforward: the suppressor adds a series of baffled chambers beyond the muzzle, and the expanding gas continues to push on the bullet’s base as it passes through those chambers. The bullet effectively gets a few extra inches of “barrel” worth of acceleration.
The change is small enough to be irrelevant for most purposes, but precision shooters notice it because it shifts their point of impact slightly. What the suppressor does change dramatically is the sound signature and the visible flash. It does not, with standard supersonic 5.56 ammunition, eliminate the sharp crack of the bullet breaking the sound barrier. That supersonic crack is separate from the muzzle blast and cannot be suppressed by any muzzle device. To get a truly quiet 5.56 rifle, you need subsonic ammunition, which means slowing the bullet to below roughly 1,100 feet per second. Subsonic 5.56 loads exist but are uncommon and sacrifice most of the cartridge’s terminal performance, since the round depends so heavily on velocity to do its job.
Measuring Muzzle Velocity at Home
Chronographs are the standard tool for measuring muzzle velocity, and they have become remarkably accessible. Optical chronographs use two light sensors spaced a known distance apart; when the bullet’s shadow passes over each sensor, the device calculates velocity from the time interval. These run from about $50 to $200 and sit on a tripod a few feet in front of the muzzle. Their main drawback is sensitivity to lighting conditions, and the occasional shooter does put a round through the device by accident.
Doppler radar chronographs, which have become popular in the last decade, mount behind the shooter and track the bullet’s velocity continuously from muzzle to target. These are more expensive but give you the full velocity curve rather than a single data point. For someone tuning handloads or comparing barrel lengths, that curve is far more useful than a single muzzle reading. A string of 10 shots through a chronograph will also reveal the velocity spread, which is a key indicator of ammunition consistency. Good factory 5.56 ammunition typically shows a standard deviation of 15 to 25 feet per second; hand-tuned match loads can get that below 10.