This article will cover the rifle as used in weaponry. This is not limited to rifles as a long arm, as the article will include pistols, shotguns, and other weapons.
Science of the Rifle
The rifle was actually invented by accident. The first rifle was created when someone cut channels or grooves into the barrel of a musket so that unburned black powder could collect in these channels making the weapon less likely to jam when loading. It was discovered by those who used these modified weapons saw that the musket ball would spin and the accuracy of the shot would increase within a certain range. Once a cylindrical bullet was used, the rifle became an extremely accurate weapon able to hit targets consistently at long ranges.
The principle of rifling is to put a spin on the bullet. When spinning the body will react to an outside force by pushing back at a right angle as compared to the spin of the object. To experience this force in action, take a bike tire off of a bicycle and get the tire spinning. Holding the axles, twist the tire in any direction you choose. The tire will resist and twist in an odd angle when compared to the reaction of the tire when not spinning. The bullet also has this effect when wind or other forces push against it, preventing the bullet from tumbling end over end in flight.
Another important effect that the spin placed upon a bullet has is that it reduces the airfoil effect that spherical bullets experience. The effect can be seen most readily when hitting a golf ball. Should the golf ball be imparted with a backspin, the ball will create a mass of air in front of and just under the ball. This mass of air will push up against the ball creating lift, and enabling the ball to travel further. Should the spin put on the ball twist to the side, a mass of air will build up on one side of the ball, pushing it left or right. If the ball where to twist so that the top and bottom of the ball are the points moving, and the front and back of the ball remain in the same position, the effect would cause lift to be present around the ball, actually pushing the ball into itself. This make the ball stable and less subject to change in its flight path. When bullets became cylindrical, the bullets held the spin longer and would not begin to spin at other angles as easily so the flight path of the bullets became even more consistent.
After the rifling of barrels was mated with a cylindrical round, the basic concept of the rifle has not changed. The changes that the rifle experienced has been the mechanism to fire it and the materials it is made out of.
Firing a Rifle
The first of many weapons to fire the rifle were based on flashpans. A flashpan was a pan attached to the side of the barrel next to the main charge. A small tube was bored so that the flashpan and the charge had a clear path to each other. Black power was placed in the flash pan and ignited. The following explosion forced energy down the tube to the main charge, which exploded and fired the bullet down the barrel. Many different means were used to ignite the power in the flashpan. The more simple methods were taking a smoldering rope and touching it to the pan. This method worked, but was cumbersome as the string could go out or the person firing the weapon would have to manually put the string to the pan, affecting aim.
The smoldering string mechanism was replaced by the flintlock design, the primary weapon used during the War for American Independence. The string as removed and a piece of flint on a spring-powered arm was introduced. Over the flashpan was place a striking plate made of steel. This plate covered the powder and allowed a place for the flint to strike and cause sparks. The flint would hit the steel hard, flipping the striking plate out of the way and forcing sparks into the flashpan, where the powder would ignite and the weapon is discharged.
The flintlock had many disadvantages. The flint did not always create sparks. The powder in the flash pan could get wet and not fire. The flint could break and require replacement in the middle of battle. The next piece of technology to be introduced was the percussion cap.
The flashpan was removed and a metal nipple with a hole drilled through it to the main charge put in its place. The arm that held the flint was modified so that a hammer would strike down on top of the nipple. The key piece to this technology was the percussion cap itself. A brass cap the size of a pencil eraser contained fulminate of mercury in the bottom of it. When struck, this mercury would explode.
To fire the percussion rifle, the user would place the brass cap on the nipple or the gun. The user would then pull the hammer back, aim and pull the trigger. The hammer would strike atop the cap and force the explosion into the drilled hole through the nipple to the main charge, firing the weapon.
It is during this time that the first multiple shot weapons appear. These were the first revolvers as well. The revolver consisted of a metal cylinder with (usually) 5 to 6 holes drilled into it along the outside of the cylinder. Within these holes were loaded a main charge and a bullet. At the end of each of these separate chambers was a nipple for a percussion cap. The cylinder was spun with each shot, allowing the user to fire many times in a row without having to reload between shots.
The first revolvers were single action, meaning that the user had to pull the hammer back manually, spinning the cylinder and cocking the weapon, then pull the trigger to fire. Double or dual action revolvers soon came about, so that the user only have to pull the trigger for the hammer to be pulled back, cylinder rotated and the weapon fired. Most modern revolvers are double action.
The next step for the rifle to take was self-contained cartridge. These consisted of a percussion area, the charge, and the bullet all contained within a brass casing. Two types of cartridges were produced; centerfire, which are common today and have the percussion cap on the rear of the cartage and centered, and rimfire, in which the percussion cap is spread along the rear edge of the cartridge all the way around.
With these self-contained cartridge systems, weapons were no longer subject to weather to the extent that the exposed powder was and opened the way for quick loading and multi round firing weapons, such as machine guns and assault rifles. Shotguns, too, can be rifled, and use an excellent example of a self-contained cartridge. The plastic shell contains the bullet (or pellets) and the charge together and in such a manner so that moisture and dust cannot enter, while the metal portion contains the percussion cap and the primer to fire the shell.
New weapons are being created all the time that use the rifling principle to stabilize bullets and other projectiles. But the future seems to point away from rifles and back towards smoothbore weaponry. The main barrels on tanks are smoothbore, not rifle, barrels. This is so that Sabot rounds can be used. These rounds fire a thin strong needle of a dense metal, tungsten, depleted uranium, or an alloy of different metals. Rifling would make the sabot spin or tumble and change the trajectory or impact point. The new linear accelerators use smoothbores, as rifling would effect the magnetic charges on the projectiles. While rifles will never leave military, police, or civilian arsenals, the future development of rifles may take a backseat as new electronic weaponry takes hold, and set aside by particle weapons or other such technology.
Fairfax County Public School IB Physics I and II
Multitude of books on the subject