Has anyone experienced where a 180gr .308 bullet reaches a optimum/max velocity before the accuracy seems to drop off?
Say a 180gr in a 300 Win Mag. From what I've seen there seems to be a sweet spot around 3050fps and once you get above 3100fps there seems to be a stability problem where seating death changes can't correct.

I load 178 Hornady ELD-X bullets with a max charge of Varget for just over 2600 fps. I only shoot 3 shot groups, but Sunday shot six, 3 shot groups from 2 different rifles and the the largest group was 5/8". The others ranged from 3/8"-1/2". All @ 100 yards BTW..

If your bullets are properly made, they are for all intents and purposes velocity independent. You do need to worry about rotation though because you do have to stabilize the bullet. The rifle is far more of a factor than the bullet.

I have seen the sweet spot at 3150fps in quite a few rifles. The more strange thing I noted is that 24" barrels were the most common on the rifles I used and tested. Recently write about 3 that I was working with at once and again, all had 24" barrels and all shot best around 3150fps with the 180gn.

I have a spare 26" .300Win barrel in my gun room but haven't wrung it out yet. The interest is there however.