There is no doubt that the Brown Bess's bullet was lethal at its full range of effective fire. In the mid-18th century, Robertson measured the speed of musket bullets on a ballistic pendulum. According to him, the speed of a round musket bullet slug was about 1804 feet per second (550 m/s). That is, the muzzle energy of the musket was about 3,500 to 4,000 joules, which is comparable to the energy of modern rifle cartridges. Modern ballistic tests have confirmed these data.