早期的燧发枪(步枪原型)口径平均13.7毫米,到19世纪60年代,大多数军用步枪口径已减小到11毫米。1942年,德国STG44突击步枪首先使用7.62毫米步枪弹。随后,前苏联的AK47,美国的M14,比利时的FNFAL等,均采用了7.62毫米步枪弹。上个世纪60年代越南战争爆发以后,东南亚的丛林地形使得M14步枪和北约枪弹的弱点充分暴露出来。美军越来越感到没有必要像“大弹头打苍蝇” The average size of the early flintlock (rifle prototype) was 13.7 mm. By the 1960s, the size of most military rifles had been reduced to 11 mm. In 1942, the German STG44 assault rifle first used a 7.62 mm rifle. Subsequently, the former Soviet Union AK47, the United States M14, Belgium’s FNFAL, etc., have adopted 7.62 mm rifle ammunition. After the outbreak of the Vietnam War in the 1960s, the jungle terrain of Southeast Asia fully exposed the weaknesses of M14 rifles and NATO guns. The US military increasingly feels no need to fly like a big warhead.