Some time near the end of the 15th century, some people began to recognize the importance of causing the bullet to spin in order to properly stabilize it. Improvements were made by August Kotter in 1520 (biographical material unavailable), who was an armorer in Nuremberg, Germany, at the time; the original person responsible for the idea is unknown or uncertain. Though several methods are presently available to cause the bullet to spin, some of them more effective than others, with the most effective method – for small arm ballistics – has been to install “rifling” inside the bore of the barrel. As the bullet moves through the bore, the bore pressure forces the bullet to take the shape of the rifling to spin at the rate of the rifling twist in the bore.