.300 Winchester Magnum
When it comes to long-range calibers, the keys are speed and mass. The 300 Win Mag has plenty of both, one of the primary reasons that the US Army has made a push to adopt it in recent years.
This popular hunting cartridge can fling a 150-grain bullet at 3,200 fps, which, as you can imagine, creates quite a bit of momentum and a predictable flight path. Given its raw power, it creates significant recoil, which can be managed by a muzzle break and proper technique.
This round is also widely available at sporting goods stores, with lots of selection to choose from. Reloading is certainly not necessary with the .300 Win Mag. If you do decide you want a very specific set of specs, you can most likely find what you’re looking for from one of the trusted ammo brands.