For extreme accuracy, what is recommended for the flash hole, even on new brass?

For extreme accuracy in handloading ammunition, unifying the flash hole is significant. The flash hole, which allows the primer's flame to ignite the powder charge, can vary in diameter and finish among different brass manufacturers. By ensuring that the flash hole is uniform—in terms of both size and surface finish—you can create a more consistent ignition of the powder charge. This leads to improved velocity uniformity and reduced variations in the trajectories of the projectiles, ultimately enhancing overall accuracy.

Uniformity in the flash hole helps minimize the potential differences in how each cartridge performs. When the flash hole is the same across all rounds, the variability introduced by ignition becomes minimized, leading to tighter shot groups and more reliable performance. Therefore, focusing on this aspect when reloading can make a significant difference in achieving extreme accuracy.