When the Europeans started to explore the seas in the 15th and 16th centuries, ships were mostly equipped with breech loaders. Scholars used to believe breech loaders were first introduced to the Ming Empire in the late September of 1517, and were copied in 1524. It is shown here, the Treason of Prince Ning during the sixth a seventh months of 1519 was the key date of breech loaders’ introduction. According to official interrogation records, Prince Ning built his first batch of breech loaders as early as the third month of 1517. And he probably obtained his prototypes from overseas trading. On the 14th of the sixth month of 1519, Prince Ning uprose. Probably to avoid illegal weapon making, one senior officer line Jun (林俊,1452-1527) who had seen breech loaders before, built a tin replica of it and asked his servants to carry it to Wang Shou Ren (王守仁,1452-1529), then Southern Qiang Xi province’s governor (南贛巡撫), in the hope he could build his own breech loaders. However Prince Ning was arrested on the 1st of the eighth month. Wang Shou Ren did nto have the luxury to use breech loaders in combat. After the battle, Wang Shou Ren let his friendly forces: Bi Hong (費宏,1468-1535), Tang Long (唐龍,1477-1546), and Wang Shou Ren’s aide Zhou Shou Yi (鄒守益,1491-1562) compose poetry to praise Lin Jun’s loyalty that made the effectiveness of breech loaders widely known among the literati. Many people who fought the treason became promoters of breech loaders, including $Tang Long, Xiao Huai (蕭淮), and Wang Shou Ren’s mentor Wang Qiong (王瓊,1459-1532). Therefore, we can say Prince Ning’s Treason was the key factor to the adoption of breech loaders in China.