[Unclenick]

To make sure commercial cartridges always fit in commercial chambers, SAAMI always gives chamber dimensions as a minimum with the tolerance being no less than those dimensions, plus some number. To ensure cartridge fit, the opposite approach is then taken with cartridges: the maximum not-to-exceed dimension is given in the drawings with a minus tolerance. In the example of rifle cases, the maximum length is given, with a tolerance of -0.020". So the .30-06 can be anywhere from 2.474"-2.494" and be within SAAMI specs. Some shooters ignore that and shorten an additional 0.015" so they never have to trim again during the normal reloading life of the cartridge. Most commercial trimmers that are fixed, though, like the Lee, will trim right at the middle of the SAAMI tolerance: 0.010" less than maximum and more than minimum.