If your talking a 6mm rem, I shoot the 70gr NBT for 600yrd f-class. They are amazing on PD if you like the red mist. They hold .25 MOA at 300yr.
I use IMR4831 48gr, Rem brass and Fedral primers. Also the 71gr Begers have shot well.
Hi your 6mm Rem 700 VLS will shoot any VLD type projectile yo to 90gr so give some hiugh BC 90gr VLD's a go and they will make 1000 yards with velocity to spare.
I use 55gr BlitzKings in the same rifle but it was a 243 and i set the barrel back and rechambered it to 6mmBR the 55's are leaving at 3400fps and have shot it past 600 yards with that load also the barrel has been choped to 22" to maki it a little handier with a Noveske KX3 Flash Suppresor that i just fitted today.