Home Forums Hunting & Shooting Ask The Gunwriters Pressure signs.

As queer as You ?




Just asking.

Jerry

Loads that behave properly in new brass can be over the edge the next go around in the once fired brass. Once again, the chrono will tell the story as the load is faster in the once fired brass.

Why would the same load be faster in once-fired brass vs new brass?

Many times a load does chronograph slightly faster in fired brass than in new brass, but it has nothing to do with higher pressure. Instead a little bit more of the energy from the powder is used in "blowing out" the new brass to fit the chamber, rather than pushing the bullet. This effect is slightly larger in fire-forming improved cartridge with new brass.

Fired brass might result in slightly higher peak pressures due to working-hardening the neck, whether through firing or resizing, resulting in the neck not releasing the bullet as easily. We know that "cold welding" of a bullet in the neck can result in higher pressures.

Or at least those are the conclusions of some shooters, including at least one pressure-lab tech I know.

My 243 win with 90gr Scenar in lapua brass, chronos 30-50 fps slower on first firing. After the first firing the cases are resized with Redding body die and necks are sized with Lee collet die. The velocities are measured with a Labradar.