The important factors of its necessity and transition were the selection of materials for bows and their combination, in particular, to find 'the elastic modulus and elastic limits against the ratio of length of the bow and cross-sectional dimension' (when the cross-section is not point symmetry, add 'the elastic modules and elastic limit against the cross-section and the direction of bending'), and 'the least power to pull and the longest flying distance,' as well as the difference of conditions such as 'shooting from the ground or from horseback,' and 'the mechanization and the ability of automatic fire.'
その変遷や必要性において重要な要因は、弓の素材の選定やその組み合わせであり、具体的には「長さ（弓丈）と断面積の比率に対しての弾性率・弾性限界」（断面形状が点対称でない場合は「断面形状と曲げる方向に対しての弾性率・弾性限界」も加味する）や「最小限の引く力と最大限の飛距離」など、条件の妥協点を見出す事にあり、その他には「地上やウマ上から矢を射る」という条件の違いや、「機械化と連射性能」などである。