My 45 year old 7mm Remington Magnum shoots 150 grain NBT or Barnes TTSX very accurately. Sighted in at 225 yards it’s point & shoot to about 340 yards and only 1.5” high at 100. Holding over with a Zeiss duplex I’ve killed stuff past 500 yards since it’s an old familiar friend. In my opinion it is the perfect long range deer cartridge. Not too much recoil for experienced hunters & kills like you hit them in the head with a sledgehammer.
All the flat shooting suggestions you’ve gotten that let you hold on hair & hit vitals at 400 have a big speed of shooting advantage over your 308 or a Creedmoor that require ranging & dialing. Modern rangefinders are an affordable necessity these days and have cut into the speed kills rifle cartridge sales but the soft kickers don’t compete for shooting quickness in that 300-400 yard range.
If you add a precise dialing scope on the 7RM it extends the range past 600 depending on wind of course.
Lots of the flat shooters will work beautifully as your longer range deer gun my favorite is the 7RM but any of them work if you reload - if not pick something you can buy ammo for easily.
