If you suspect the rifle isn't chambered as stamped. I would go to a gunsmith and see what they can tell you. They will likely steer away from advising on something if they think it's potentially unsafe.Need help I purchased a custom model 70 pre64 in 8mm mag when i shot it it blow out the brass any idea on what the previous owner rechambered the gun to looks like a beltless case ???
Rather than unsafely guessing, I would use the action and rebarrel it but that's just me. Even if you stick the the 8mm, at least you know what you have.
The information you provided is very vague. It could be as simple as it needs a good cleaning, or may be much more complicated.
Stay safe.