I have a 18” 6.5 prc and 11” 6mm creed. For the creed I have a new thunder beast dominus coming. I don’t know if I’d do another creed tho. Think the bra would be better. It runs a 110 at 2550. The 18” prc runs a 135 at 3000.
With a 400m/450yard requirement, it is questionable he would have enough energy at the outer range to be an effective game cartridge. It does depend on what he is shooting at that range however. A Fox is much different than a Russian Boar or big Bear.300 Blackout. Very versatile round and you can make your own brass out of spent .223. I've running an 9" bolt action remy 700 that is a stupid quiet suppressed and a short handy package.
After page 1 said 200 lb animals at 450 yards I was a little flabbergasted to see 300 blk. Same with grendel IMODear all, many thanks for all commets. I will sumarize somehow my decision. As I do not want to use AR platform of any kind and I want subsonic only as option for 10% of hunting related shooting, so this somehow kicks out anemic close range rounds like 300 BLK or 338 Spectre and also AR10 calibers like 338 creedmore or 375 raptor. At the end it will be 338 Federal or 338 RCM, based on what action I will use, or I will say to old greedy self that the 308 I already have altough not perfect, still more then good enough for what I need.