Here’s what I say, and I guess this is sorta more like my combat style speaking here…
Aim for 500 yards. Everybody else has trouble shooting past 300 yards even if they have a good long range rifle.
The .50cal will probably still be going about 650-700 m/s out at 500 yards… it will have the legendary damage and penetration that its come to be known for. This is the real reason why you get a .50cal, so you can kill truck engines, shoot through a railroad track, and shoot through sandbags. Military has exploding rounds, and thats something you dont have.
This is a real treat because in the post-SHTF nazi-commie gestapo boot america, you can kill those people, who are escorting american citizens at gunpoint onto the cattle cars to be mechanically exterminated, because they’re too infirm to be retrained into effective slaves. Their body armor and light armored vehicles wont stand up to your rifle, and other resistance fighters will rely on you.
Exceptional range is a good bonus, to be sure, but there are lesser rifles out there which are cheaper and even more accurate for that kind of distance (in fact there are some calibers like .416 Barrett and .408 Cheytac which are even more devastating than a .50 out at 1500m+).
But back to the story, for 500 yard shooting you only need a standard scope, anything fancy or with bells and whistles is just going to be distracting. And since you would be using this to shoot larger-than-human size targets alot of times, or just some guy standing still at a guard post, it doesnt even need much magnification.
Get a 4x or 10x Scope.
Preferrably with optics/reticle that are self-illuminating so you can see the crosshairs easily but you dont need to feed it with batteries.