I use a 50 yard zero for two reasons:
- I use the 300 AAC almost exclusively with a 220 gr bullet, so it’s a subsonic load. The muzzle velocity is right around 1030 feet per second and the effective range of the subsonic 300 AAC is right about 350 yards or 320 meters. A 50 yard zero is optimal given the optic I use. (More on that...)
- I use an optic that is calibrated in one minute of angle (MOA), per click, with a maximum of 55 clicks or 55 MOA. Making an elevation adjustment to engage a target at 350 yards, with a 50 yard zero, requires 47 minutes or 47 clicks, so I am well within the operating range of my optic, and I don’t need multiple turns on the elevation turret. Where you zero is a personal choice driven by your choice of optics and how you shoot; however, it is generally best to zero so that you minimize use of the elevation turret. You don’t want to sit there and count turns because you tend to lose track of where you’re at. Keeping your adjustments within one turn of the turret is generally considered a reasonable strategy.
As you can see, your point of zero should be based on a pairing of the caliber/load and the performance characteristics of your scope.
The best thing you can do, is find your comfort zone for the type of shooting that you are going to do, but remember that the limiting factor is your optic. If you plan on using the 300 AAC in its full powered supersonic load, you may want to zero your rifle at 100 yards or 300 yards. Once again it will depend on your optic, reticle type, etc. Experiment!