A cannon works by trapping rapidly expanding gas in a sealed metal tube and using that pressure to launch a projectile at high speed. The basic principle hasn’t changed in over 600 years: burn a propellant in a confined space, let the pressure build, and direct all that energy in one direction. What has changed is every detail of how that sequence plays out.
The Firing Sequence Step by Step
The process starts with loading. A projectile is pushed into the front of the barrel (or breech, in later designs) until it seats firmly against the interior. Behind it, the propellant charge fills the chamber. In early cannons this was loose black powder; later designs used measured charges in cloth bags or metal cartridge cases. The key is that the projectile and the closed breech create a sealed chamber with no easy escape route for gas.
Ignition kicks off a chain reaction. A small, easily lit primer creates hot gas and burning particles that flow into a larger igniter charge, which in turn lights the main propellant. The flame spreads across the surface of every propellant grain until the entire charge is burning. This happens in a fraction of a second.
As the propellant burns, it generates an enormous volume of hot gas. Because the chamber is sealed on all sides (the breech behind, the projectile in front), pressure climbs rapidly. Once it exceeds the friction holding the projectile in place, the projectile begins to move. Pressure continues to rise even as the projectile accelerates down the barrel, reaching a peak partway through the bore. After that peak, the gas is expanding into a growing volume behind the moving projectile, so pressure gradually drops. But it’s still pushing. The projectile continues to accelerate all the way to the muzzle, where it exits at its highest speed.
The relationship between peak pressure and how far the projectile has traveled determines the final muzzle velocity. A longer barrel gives the gas more time and distance to push, which is why longer cannons generally produce higher velocities than short-barreled mortars using the same charge.
Why the Barrel Fit Matters
In the age of muzzle-loading cannons, the cannonball was always slightly smaller than the bore. That gap, called windage, was necessary so the ball could be loaded from the front. But it also let gas leak around the projectile, wasting energy and reducing both range and accuracy. A rule of thumb held that windage should be about one-fortieth of the bore diameter. For a barrel with a 2.5-inch bore, that’s roughly 0.06 inches of clearance.
Too much windage and the cannon just coughs out its shot in a cloud of smoke, with gas rushing past the ball instead of pushing it. Hobbyist experiments with a 2.5-inch bore cannon firing a 2.25-inch ball (a quarter-inch gap) showed dramatically worse performance compared to a tightly patched projectile. The sound of impact at 150 yards, the flight time, everything suffered. Wrapping the ball in a cloth patch to seal the gap produced noticeably better results, the same trick riflemen had used for centuries.
Modern artillery solved this problem with obturating bands: rings of soft metal or plastic around the projectile that expand under pressure to seal the bore completely. No gas escapes, and every bit of energy goes into pushing the projectile forward.
How Rifling Changed Everything
Early cannons had smooth bores, meaning the inside of the barrel was a plain cylinder. A round ball leaving a smoothbore tumbles unpredictably in flight, which limits both accuracy and effective range. Smoothbore weapons become essentially useless beyond about 100 to 150 meters for any kind of precision.
Rifling, a set of spiral grooves cut into the barrel’s interior, solved this by spinning the projectile as it travels down the bore. That spin stabilizes the projectile in flight the same way a football spiral does. The accuracy gains are dramatic. In comparative tests with small arms (which follow the same physics), rifled weapons hit their target 97% of the time at 90 meters versus 74% for smoothbores. At 270 meters, the gap widened to 46% versus 14%. Rifled weapons maintained useful accuracy out to several hundred meters, while smoothbores were effective only at close range.
Rifling also meant cannons could fire elongated, aerodynamic shells instead of round balls. These carried more mass, flew farther, and cut through the air more efficiently. The combination of spin stabilization and better projectile shape transformed artillery from a short-range battering tool into a long-range precision weapon.
Types of Projectiles
The ammunition a cannon fires has always been chosen to match the target.
- Round shot: Solid iron or stone balls, the most basic cannon projectile. Iron balls pulverized stone and brick walls, making them ideal for siege warfare. Stone cannonballs delivered a heavier impact shock that could bring down large sections of wall at once. A common siege tactic was to undercut the base of a wall with iron shot, then use large stone balls to collapse what remained above.
- Grapeshot and canister: Clusters of small iron or lead balls bundled together for loading but designed to separate as they left the muzzle. They spread out like a giant shotgun blast, making them devastating against massed troops at short range.
- Explosive shells: Hollow iron balls filled with gunpowder and fitted with a fuse that had to be lit just before firing. These appeared in the 15th century and were the ancestors of modern exploding shells. They were notoriously dangerous to the crew, as they could explode prematurely or jam in the barrel. Because of this risk, early explosive shells were used mainly in short-barreled mortars, where the projectile spent less time in the tube.
How Ignition Systems Evolved
The earliest cannons were fired by touching a burning slow match (a treated rope that smoldered continuously) to a small hole drilled in the breech called the touchhole or vent. This was crude and unreliable, especially in wind or rain. The gunner had to hold the match with one hand while managing the cannon with the other.
Mechanical locks came next. The matchlock used a pivoting S-shaped arm that held the burning match and swung it into the touchhole when the gunner pulled a lever. Spring-powered versions added a trigger mechanism, freeing the gunner’s hands. The wheel lock, borrowed from household fire-starting tools, used a spinning steel wheel against a piece of iron pyrite to create sparks, eliminating the need for a burning match entirely. The flintlock refined this further, striking a piece of flint against steel to produce sparks reliably and quickly.
The real breakthrough was chemical ignition. Percussion-sensitive compounds like mercury fulminate could be detonated by a sharp blow, meaning no open flame or spark was needed. Early versions included fulminate-filled tubes about 5/8 of an inch long, inserted at right angles to the bore where the old vent had been. The gunner struck the tube with a hammer, and the fulminate’s flash ignited the main charge. This worked in any weather and fired almost instantly. Percussion caps, small metal cups filled with fulminate that fit over a nipple on the breech, became the standard system by the mid-1800s and remain the underlying principle behind modern artillery primers.
Managing Recoil
Newton’s third law means the cannon experiences the same force as the projectile, just in the opposite direction. Early cannons simply rolled backward on their carriages when fired, and the crew had to wrestle them back into position for the next shot. This was slow, exhausting, and dangerous.
Modern artillery uses hydraulic recoil brakes to absorb that energy. When the cannon fires, the barrel slides backward along rails while forcing fluid through narrow openings inside a hydraulic cylinder. The resistance of the fluid passing through those restricted channels converts the violent kick into controlled, manageable motion. The barrel then returns to its firing position, often driven by a compressed-gas recuperator. This system lets the gun stay aimed at its target between shots, dramatically increasing the rate of fire.
Bronze Versus Iron
For centuries, cannons were cast from either bronze or iron, and each material had clear tradeoffs. Iron was cheaper and lighter, which made it the practical choice for most fortifications. Bronze was more expensive but lasted longer and failed more gracefully. A bronze cannon that was wearing out would bulge or deform, giving warning before it burst. An iron cannon could crack without warning. Bronze could also be melted down and recast if a gun was damaged, making the metal itself a reusable asset. Cannons from the same fort might range from small 2-pounders to massive 32-pounders, named for the weight of the ball they fired.