[doug_porsche]

I am as far from an expert as you can get.
Your post just made me curious.

It looks like 5000 fps is, hmmm, ambitious, by about 40%ish

repeating what I see in my random sample....

https://www.ammunitiontogo.com/lodge/308-ballistics/
https://aimingexpert.com/what-is-the-muzzle-velocity-of-a-308-round/
https://blog.cheaperthandirt.com/the-fastest-308-win-on-the-market/
https://rifleshooter.com/2014/12/308-winchester-7-62x51mm-nato-barrel-length-versus-velocity-28-to-16-5/