Bullet trajectory is the curved path a bullet follows from the moment it leaves the barrel until it reaches its target or comes to rest. Despite what action movies suggest, bullets don’t travel in straight lines. The instant a bullet exits the muzzle, gravity begins pulling it downward while air resistance slows it forward, creating an arc that drops increasingly steeply over distance. Understanding this arc is fundamental to accurate shooting at any range.
The Three Forces That Shape a Bullet’s Path
A bullet in flight is essentially a small object governed by the same physics as anything else moving through the atmosphere. Three primary forces determine where it ends up.
Gravity pulls the bullet downward at a constant rate, regardless of how fast it’s moving. This is the dominant force shaping trajectory. A bullet fired perfectly level begins falling the instant it leaves the barrel, and the longer it’s in the air, the more it drops. At close range the drop is tiny, but it compounds dramatically with distance.
Air resistance (drag) acts opposite to the bullet’s direction of travel, steadily robbing it of speed. Every air molecule the bullet strikes takes a small fraction of its energy. As the bullet slows, gravity has more time to pull it downward before it reaches the target, which makes the drop curve steepen the farther the bullet flies.
Wind pushes the bullet sideways, up, or down depending on direction. A crosswind shifts the bullet laterally and can change its angle relative to the air. A tailwind or headwind changes the bullet’s effective speed through the air, altering how much drag it experiences and, in turn, how much it drops.
How Far a Bullet Actually Drops
To put real numbers on this, consider a common rifle cartridge: a .308 Winchester firing a 147-grain bullet at about 2,780 feet per second. At 100 yards the bullet has already dropped roughly 8 inches below the line of the bore. At 200 yards, that drop grows to around 23 inches. By 300 yards, it’s nearly 47 inches, or close to four feet.
This is why shooters don’t aim directly at a target. A rifle’s scope is angled slightly downward relative to the bore, so the bullet’s arcing path crosses the line of sight at a specific distance (called the “zero”). Before that distance, the bullet is still rising relative to your aim point. After it, the bullet falls below it. Choosing where to set your zero is one of the most practical decisions in shooting, because it determines where along the arc your bullet and your aim point align.
Maximum Point Blank Range
Hunters use trajectory data to simplify aiming through a concept called maximum point blank range (MPBR). This is the farthest distance at which a bullet stays within an acceptable window above or below your point of aim, so you can hold dead center on the target and still land a hit without adjusting for drop.
For most North American big game, that acceptable window is about 6 inches total: 3 inches above and 3 inches below where you’re aiming. A quick way to estimate MPBR is to divide the bullet’s muzzle velocity (in feet per second) by 10. A bullet leaving the barrel at 2,800 fps gives you an estimated MPBR of 280 yards. Inside that distance, you aim at the center of the animal’s vital zone and the trajectory stays within the kill zone without holdover adjustments. Round-nosed or spherical projectiles lose about 20% of that range compared to sleeker designs moving at the same speed, because they encounter more drag.
Why Bullet Shape Matters
Not all bullets slow down at the same rate. A blunt, flat-based bullet plows through more air than a sleek, tapered one, and these differences are captured by a number called the ballistic coefficient (BC). A higher BC means the bullet resists drag more effectively and holds its velocity longer, resulting in a flatter trajectory.
Manufacturers describe bullet performance using standardized drag models. The two most common are G1 and G7. The G1 model is based on a flat-based bullet with a relatively short nose and works well for traditional hunting and target rounds. The G7 model is based on a long, boat-tailed bullet with a very streamlined profile and is more accurate for predicting the flight of modern low-drag designs. Using the wrong model for your bullet type can introduce meaningful errors in trajectory predictions, especially past a few hundred yards.
How Air Density Changes the Arc
The same bullet fired from the same rifle will follow a different trajectory on a hot summer day than on a cold winter morning. The reason is air density. Temperature, altitude, barometric pressure, and even humidity all change how many air molecules are packed into a given volume of space. Fewer molecules means less drag, which means the bullet retains more speed and drops less.
Shooting at high altitude is a good example. At 5,000 feet above sea level, the air is noticeably thinner than at sea level. A bullet encounters less resistance, arrives at the target faster, and has less time to drop. The result is a higher point of impact than you’d see at the same distance in denser, low-altitude air. Temperature works similarly: warm air is less dense than cold air, so hot conditions produce slightly higher impacts. These differences are small at short range but can shift a bullet’s impact by several inches at 500 yards or more.
Spin Drift and Gyroscopic Effects
Rifling, the spiral grooves cut inside a gun barrel, imparts spin to the bullet. This spin stabilizes the bullet in flight and prevents it from tumbling, which is essential for accuracy. But that same spin introduces a subtle sideways drift called gyroscopic drift, or spin drift.
A bullet spinning clockwise (from a barrel with a right-hand twist, which is the most common) will gradually drift to the right. A counterclockwise spin drifts left. This happens because the bullet’s spin axis and its actual direction of travel slowly diverge as the bullet arcs downward under gravity, creating a small sideways force. At typical hunting and target distances under 500 yards, spin drift is minor enough to ignore. At 1,000 yards and beyond, it becomes a real factor that precision shooters account for in their calculations.
Shooting Uphill or Downhill
A common misconception is that shooting uphill makes a bullet hit high while shooting downhill makes it hit low. In reality, bullets hit higher than expected in both cases.
The reason is that gravity’s ability to bend a bullet’s path is greatest when the bullet travels level, perpendicular to the Earth’s pull. When the bullet’s path is angled steeply up or down, gravity acts more along the bullet’s line of travel (affecting its speed slightly) and less across its path (which is what creates the visible arc). The result is a straighter flight path and less drop than the shooter would see on flat ground at the same distance. If you don’t account for this, you’ll aim too low for the actual conditions and your bullet will land above where you expected. Shooters compensate by using the horizontal distance to the target rather than the actual line-of-sight distance when calculating drop.
The Coriolis Effect at Extreme Range
At distances beyond about 1,000 meters, the Earth’s rotation becomes a factor. The Coriolis effect causes a bullet’s impact to shift slightly because the Earth literally moves beneath the bullet during its time in flight. In the Northern Hemisphere, this shift pushes the impact to the right; in the Southern Hemisphere, to the left. The magnitude depends on latitude, the direction of fire, and the bullet’s time of flight.
For shots under a few hundred meters, the effect is negligible. But at 2,000 meters, it can shift the impact point enough to cause a clean miss on a human-sized target. Precision long-range shooters use ballistic calculators that factor in the shooter’s latitude, the compass direction of the shot, and the bullet’s flight time to correct for this shift.
Trajectory in Forensic Investigation
Trajectory analysis isn’t only relevant to shooters. Forensic investigators reconstruct bullet trajectories to determine where a shot was fired from, often as critical evidence in criminal cases. Traditional tools include trajectory rods (rigid dowels inserted into bullet holes to show the angle of impact) and lasers projected along the bullet’s path to trace it back toward its origin.
More advanced methods now use medical imaging and 3D software. Investigators can take CT scans of a gunshot wound, use specialized imaging tools to trace the bullet’s path through the body, mark entry and exit points, and measure trajectory angles across multiple anatomical planes. That data can then be imported into 3D modeling software to reconstruct the scene, placing the wound trajectory into the context of the physical environment to estimate the shooter’s position, elevation, and distance. These digital reconstructions are increasingly used alongside physical evidence to build a more complete picture of what happened.