Any decent .308 bolt action with adecentscope will get you to 500. Savage has guns that are plenty accurate enough, though they sometimes have issueswhen run hard. Still takes some ammo and range time to be confident, though.
Yes - my Savage 308 gets me to 1000 (with the right ammo), and 500 is very doable with a 308. Actually, for target shooting, an AR-15 can do 500 too.
My thoughts on the original subject - if you intend to use the guns in possible times of unrest, I’d go with common calibers. 9 mm, 357 mag/38 spl, 40 cal, 45 ACP, 223/5.56, 308, 12 gauge shotgun.
If you want to reach out much longer, and don’t mind the cost, 50 BMG bolt action guns will do the trick, but you mentioned 500 yards and the 50 isn’t necessary for that, unless you’re looking to disable vehicles.