Worldwide. Anti communists should be chompin’ at the bit for an opportunity to go there as a volunteer sniper. Bring their own high-powered rifle. Nah, no skin in the game. They’d have to be older and ready to die. Affairs in order and no real family to leave behind. The world is full of these guys especially the moozlem community.
One universal caliber. I say .223. Cheap and popular. I remember the Russian ammo going for a cheap 21 cents per round.
For sharpshooting use 7.62x54R in scoped bolt guns for ease of logistics.