In cartridge manufacturing, the flash hole is "punched" into the brass. While this is the least expensive method, it has many shortcomings and inconsistencies. The flash holes, therefore, are of different sizes and shapes. The most detrimental to accuracy are the irregular "breakouts" and "burrs" on the inside. This will cause "shot-to-shot" differences in Primer "Flame Fronts", causing inconsistent pressure/velocity and, thereby, loss of accuracy. Bench Rest Shooters have been uniforming flash holes since 1969.