Your Pakistani ammo is probably Berdan primered. Most military surplus Berdan primered ammo from pre-1980's is corrosive. There is a salt-like substance in the primer to stabalize it. Unfortunately any of the primer residue that sticks to the inside of your barrel or bolt will draw moisture to itself. This can lead to rusting. Clean your rifle soon after firing and it will not be a problem. Soon, depends on your humidity. I live in the Mojave, not much of an issue, here. Some people use Windex (ammonia based cleaner nutrilizes the salts), Hoppes #9 works very well, some people use plain old water (the salts are microscopic and dissolve easily). Follow up with a light coating of oil and you will be fine.