Scorch please explain +/- 4" MaximumPoint Blank (MPB) trajectory
I ran some numbers for you using Nosler Accubond 180 gr bullets with a BC of .507
If you zero your 300 at 300 yards your bullets will be 3.3" high at 100 yards and 3.9" low at 350. About 9" low at 400 yards.
This used to be a common way to zero, but there are better ways with todays technology.
I use a scope with long range dots. With your 300 mag you simply zero the crosshairs at 200 yards, you will only be 1.2" high at 100 so you won't have to remember to aim low on the shots you are most likely to take. There are dots on the vertical post below the crosshairs. The 1st dot will be your 300 yard zero, the 2nd will be your 400 yard zero, and where the post tapers from thick to thin will be your 500 yard zero.
On non-magmum rounds such as 30-06 you zero at 100 and each dot corresponds to 200, 300, and 400. They are very accurate and simple to use.