The Evolution Of The Rifle

Some early rifled guns were created with special barrels that had a twisted polygonal shape, in particular the Whitworth rifle was the first to be made with the intention of spinning the round for the use of as a "rifle". Specially made bullets were designed to match the shape so the bullet would grip the rifle bore and take a spin that way. These were generally limited to large caliber weapons and the ammunition still did not fit tightly in the barrel. Many experimental designs used different shapes and degrees of spiraling; one widely produced example was the Metford rifling in the Pattern 1888 Lee-Metford service rifle. Although uncommon, polygonal rifling is still used in some weapons today with one example being the Glock line of pistols (which fire standard bullets). Unfortunately, many early attempts resulted in dangerous backfiring, which could lead to destruction of the weapon and serious injury to the person firing.
• Barrel wear
As the bullet enters the barrel, it inserts itself into the rifling, a process that gradually wears down the barrel, and also causes the barrel to heat up more rapidly. Therefore, some machine-guns are equipped with quick-change barrels that can be swapped every few thousand rounds, or in earlier designs, were water-cooled. Unlike older carbon steel barrels, which were limited to around 1,000 shots before the extreme heat caused accuracy to fade, modern stainless steel barrels for target rifles are much more resistant to wear, allowing many thousands of rounds to be fired before accuracy drops. (Many shotguns and small arms have chrome-lined barrels to reduce wear and enhance corrosion resistance. This is rare on rifles designed for extreme accuracy, as the plating process is difficult and liable to reduce the effect of the rifling.) Modern ammunition has a hardened lead core with a softer outer cladding or jacket, typically of an alloy of copper and nickel - cupro-nickel. Some ammunition is even coated with molybdenum-disulfide to further reduce internal friction - the so-called 'moly-coated' bullet.