Milsurp OAL vs SAAMI OAL

Matt_X wrote:   Some place I recently read an explanation of why the military velocities WW2 era were much further out.

The early digital ballistic chronographs were built with vacuum tube logic for counting a crystal time base. The crystals were ultimately traceable to the old Bureau of Standards. I don't know the details of the proximity sensing coil system that was developed between the wars for use in place of breakwires as part of a portable system. I only know that, like the electromechanical devices from the 19th century, its response was slow. Without digital logic, the analog instruments need to make a big enough trace or meter movement to resolve small bits of time. That's why the first screen (wire or coil) was at 6 feet and the second was way out at 150 feet, for an average of 78 feet. That's where the military 78 foot rifle velocity measuring distance came from.
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Nick