22 Hornet, which requires a tougher barrel than a. 223 Remington, which requires a tougher barrel than a. 220 Swift requires a tougher barrel than a. To give a satisfactory service life, barrels for high velocity cartridges must me made from tougher and harder steel than barrels for lower velocity and pressure cartridges. Falling velocity, compared to a new barrel, is a sign that a barrel is wearing out.
This increases the rate of erosion and also lowers muzzle velocity. Heat is bad for barrels, so letting a barrel cool between shots extends barrel life.Īs erosion occurs more powder gas blows past the bullet before it can seal the bore. Erosion gradually moves down the bore with use and can be seen with the naked eye as it becomes more severe. Erosion starts in the barrel's throat, where the rifling begins, as this is where the heat from the burning powder is greatest it literally melts away the steel a tiny bit with every shot. For example, I have read that, according to Hornady technicians, the accurate barrel life of a 6.5mm PRC rifle (143 grain bullet at 2960 fps MAP 65,000 psi) is about half that of a 6.5mm Creedmoor rifle (143 grain bullet at 2700 fps MAP 62,000 psi)-about 1500 rounds versus 3000 rounds!īarrel wear is due to erosion from the extreme heat and pressure caused by firing a cartridge. 30-378 Weatherby, are notorious barrel burners. The higher the pressure and velocity of a cartridge (pressure and velocity usually increase together), the more powder a cartridge burns and the smaller the bore through which the burning powder is forced, the faster it will wear out a barrel.īig capacity, small bore cartridges operating at very high pressure, such as the 6.5mm PRC. Rifle barrels are usually made from steel alloys called ordnance steel, nickel steel, chrome-molybdenum steel, or stainless steel, depending upon the requirements of the cartridge for which they are chambered. These very heavy barrels, designed for extreme accuracy, are most commonly seen on target rifles and varmint rifles. Some barrels, called "bull barrels" are not tapered at all. Tapered barrels are greater in diameter at the chamber than at the muzzle, because when a cartridge is fired, the pressure is highest at the chamber end. This lightens the barrel by removing excess metal. The outside of the barrel is tapered by turning it down to whatever contour is desired. The distance across the grooves is called the "groove diameter." This varies depending on the caliber, but measures. The rifling grooves are then cut into the bore. It starts as a steel bar, which is then drilled and reamed to the "bore diameter" of the cartridge for which it is to be chambered. A rifle barrel is usually a long (16 to 30 inches), tapering, tube made of steel with thick walls.