Calhoon cartridges are a class of .19 caliber cartridges created by James Calhoon, a firearms designer with an in interest in .19 caliber cartridges. Calhoon began working with .19 caliber after his interest was piqued from learning about British sub-caliber rifle trials in the early 1970s. .19 caliber rifles have thicker rifling than .17 and .20 caliber rifles, which helps the barrel stay clean longer and improves barrel life.