If it is an early model 39 they are not proofed for high speed ammo. After a short time the bolt will break. Check with the Marlin collectors club for details. Don't shoot anything but standard velocity ammo till you get the information. I speak from vast experience. I broke 3 bolts on early 39's before I learned. In those days early replacement bolts could only be secured by purchasing a wreck rifle and parting it out. They are now close to impossible to find replacement bolt. I have purchased 2 early 39's without bolts as they had been parted out by people needing a bolt.
What's "early" pre war?
