He might give you a history lesson:
The Garand was originally going to be chambered in the . 276 Pedersen, but the logistics of changing all of the infantry's guns (including machine guns) to a new round was judged cost-prohibitive, so the Garand was chambered in . 30-06
The M1 was supposed to be basically a 7mm.
Back on topic, I think peterk123 would be better served by the non-manbun .223. He's going to have opportunities to pop smaller varmints for rancher friends. 6.5 CM would be a bit much for gophers (ground squirrels), woodchucks, and possibly praire dogs.
It is not guaranteed every shot will be within 300 yards, and an open field will probably be windy.
The best cartridge, in this case and keeping it somewhat small, is 6.5cm.
Hate on it, but it can do everything a 556 and 308 can do, but better and easier. With low recoil, plenty of guns available and plenty of good ammo available.