7.62×51mm NATO in metric : Note: The product of mass and velocity is a quantity called, in modern physics, "momentum".
John "Pondoro" Taylor, an ivory hunter who over his career shot over 1,000 elephants along with a variety of other African game and who is renowned for writing two books about rifles and cartridges for African hunting, devised the Taylor KO factor to place a mathematical value on the concussive effects a cartridge and bullet would have on an elephant, specifically from a shot to the head when the brain is missed, a "knock out" meaning the elephant was sufficiently stunned by the hit that it would not immediately turn on the hunter or flee.
[4][6] The Taylor KO factor conforms to the observations and experiences of Taylor who, along with other very successful elephant hunters such as Deaf Banks, Pete Pearson and Jim Sutherland, preferred large heavy bore rifles for elephant hunting in close country.
[2][4][9] Whilst most acknowledge the originality of the formula and Taylor's broad big-game hunting experience with a wide variety of cartridges, the Taylor KO factor is source of some debate amongst modern gun writers, some describing it as peculiar, antiquated, inaccurate and an unfounded theory, others stating it is a useful tool but stressing that should not be used in isolation when choosing a big-game hunting cartridge, whilst others still say their experiences tend to support the formula.
[1][2][3][13] Taylor himself acknowledged this, stating "in the case of soft-skinned non-dangerous game, such as is generally shot at medium to long ranges, theoretical mathematical energy may possibly prove a more reliable guide" and that his formula was designed to measure a cartridge's performance against the large, thick skinned, big boned elephant.