Starting load development with virgin brass and barrel is worthwhile to a certain extent. It’s good to get an idea of what your ideal charge weight and seating depth will be.
but as others have stated, once the barrel speeds up you will see an increase in speed.
There will also be changes, although slight, with fireformed vs virgin brass. The virgin brass was sized by the manufacturer, your fire formed brass was sized by your rifle’s chamber and then by yourself with your dies. Now if you’re only using your gun at 100-200 yards for hunting, these differences will not be significant. If you plan on chasing groups on paper or shooting out further, those changes are significant.
I’m obsessed with finding the perfect load and I’m aware that I’m reaching the point of diminishing returns, but to me it matters.
For example, my 20” proof 6.5 cm barrel sped up ~100 FPS near 180 rounds. Before it sped up, my ES was hovering around 12 FPS and I was ok with that because I was on virgin brass still. But I tried shooting a black buck doe at 500 yards with the gun during the speed up process and I shot just over her. I realized what was going on later that day when I was shooting at rocks far away so the rest of the trip I kept all my shots within 200 yards because I did not know what my velocity was.
With the barrels new speed settling in, I did not change the load but I noticed the ES was around 20 FPS and group moved from 1/2”-3/4” groups. I’ve gone outside the optimal range of my node.
I finally have all my brass formed and I plan on doing a final development with the barrel broken in and the formed brass. In other guns, I’ve noticed a difference with formed brass vs virgin, but again, it’s all relative to what you’re wanting to achieve.
BTW, my father in law bought a Ruger American in 6.5 cm and he wanted me to mount his scope, zero it with factory ammo, and put a timney trigger in it. Before shooting it I was skeptical of its potential. But I will be dammed if that gun shoots 1/2” or less groups with factory 140 eldm ammo. It’s a phenomenal gun and I’m sure you will enjoy yours as well!