recently bought a beautiful 1943 mosin-nagant in fantastic condition! got it with a lot of surplus ammo included, but im wondering if its better to use modern ammo so i dont have to deal with the corrosive salts from the surplus primers? or does the surplus ammo work best in it?
That might be a question for your local gunsmith, as its condition will determine if the breech can handle modern loads. Another option is to fire a lower powered modern load.