Has anybody had to add powder to once fired brass after doing load development on new brass? Curious I'm having a debate of adding .1 gn to my once fired brass due to it now having a greater case capacity 28 nosler.
No experience with that caliber, but I can tell you that my 260 shoots same with either. I have not adjusted loads. There is about a 15-20 fps GAIN in velocity shooting 1x brass over new. However, it is a minimal size chamber. Others with larger chamber may have different results.
I full length size all of my cases, including my new ones and I have not seen that. Not positive if there is a correlation, not having done any kind of study, but it seems to make sense that there would be.
The gases upon firing are not only used for propelling your projectile into and out of the barrel, but they are also used to expand the brass to the chamber. That's where your seal comes from, and why we use a brass alloy tuned to a plasticity which is malleable during firing and keeps gas from escaping the closed system of the case to bore. Virgin brass is typically fully sized and will require a bit more gas to be used just to expand the case. That's compared to a fired case which presumably has been sized to some extent, but not as much as a virgin case. This translates to virgin brass yielding lower velocities than fired, sized cases.
I typically get 10-20 FPS greater velocity with fired, sized cases versus virgin Lapua 6.5 CM brass.