In a SHTF I am not sure there will be many snipers. There needs to be a reason for the sniper to shoot you. He will only shoot you if he sees anything you have that he wants. In a SHTF times there will be to many people everywhere for a sniper to be shooting everyone, to much ammo.
Now if it is the government snipers shooting people for no reason but to kill people then yes they have the ammo.