The Physics of Bullets: Why a Modern Gun Shoots 10 Times Farther Than its 19th Century Counterpart

Old smoothbore guns, which were loaded with bullets that looked more like balls than torpedoes, had an effective range of about sixty yards. A relatively small engineering change, which took its lead from physics, increased the range tenfold. What could make anything work that much better?

Military guns in the Victorian era had long barrels, and were likely to jam as crud accumulated in the barrel — but what really frustrated their owners was their range. By the time people got about sixty yards away from their target, they might as well be shooting at the ground. Frequently, they were.

But a small change to the bullet and the barrel of the gun — with no change in the other mechanics or loading procedure — increased their range to six hundred yards. What did it take?

First, it took a bullet that looked more like our modern idea of a bullet: an oblong cylinder with a rounded tip. Secondly, it took a set of grooves inside the barrel of the gun that curved like the stripes on a candy cane. This was rifling. The effect of rifling on a bullet was well-known. Even archers had twisted the feathers in their arrows to get their arrows to fly true. Early rifles, though, had a more complicated loading procedure that precluded their widespread military use. Once rifling was integrated with old designs, everything changed.

The rifling on a gun barrel twists the bullet so it spins as it flies. If the bullet doesn't spin as it flies, it only shoots straight and fast if it keeps its body exactly in line with the path of its flight. If its body goes out of line, due to a slight wobble as it leaves the barrel or anything else that might nudge the tip sideways, it tumbles end over end. You can see this with any symmetrical oblong object. Push directly behind it, along its axis of symmetry, and it will move straight. Nudge the front a bit to the side but keep moving in the same direction, and it will just spin around and around.

Get the bullet spinning, and different forces come into play - forces like angular momentum. If the bullet is spinning fast enough, it will stop behaving like a a stationary oblong object and start behaving more like a top. Nudge a stationary object and it'll fall over. Nudge a spinning top and it won't. It often won't even be nudged out of place. Instead, it will describe a little circle with its tip. This is called precessing. Precession is what a spinning bullet does as it moves through the air. Instead of cartwheeling end over end, it keeps going along the path on which it was shot, while the tip is just tooling around in a little circle. This is less than ideal. And ideal bullet it perfectly aligned with its course. But when things get less than ideal — and they frequently do — the spin keeps the bullet going along its course with nothing more than a slight wobble. This difference, a spinning bullet, allowed a long shot that was ten times more accurate than previous smoothbore guns.

Whether or not accurate guns were a boon is up for debate. But it's amazing how one simple change in a design allows for such a massive change in performance.

Via University of Houston and Schuemann