US Patent 10948277 Cartridge and chamber gauges

A gauge with two probes measures a rifle chamber to determine the distance from the center of the shoulder to the start of the bore. A gauge with two holes measures a loaded cartridge to determine the distance from the center of the shoulder to the place on the bullet where the cross sectional diameter is the same as the bore of the rifle. The difference between these two measurements is bullet jump: the distance the bullet will move, upon firing, before it engages the rifling of the barrel. These same tools, properly sized, also provide a unique and convenient means for determining the cone angle of any conical surface.