Rust in a Mosin us usually the product of corrosive ammo X incomplete cleaning X exposure to moisture = Rust. If you eliminate any one of these your should not have an issue.
The salts from the corrosive primer collect moisture which rusts the part. Clean it properly, oil it well, and store it in a dry location and it won't rust. I have a room full of these old rifles that I shoot often, with corrosive ammo, and I never have a problem with rust or corrosion.