I may have heard of this happening once... A rat's claw ended up catching on the snake and cut it so bad it died?? It is the only incident of a f/t rat killing a snake I've ever heard of. It sounded like a one time thing. I feed my balls medium rats too and this has never happened, and I wouldn't think this has happened to most others either. I've never heard of breaking limbs as a precaution... You could feed him small rats if that makes you more comfortable. I probably wouldn't feed an adult male medium rats if you feed on a weekly schedule anyway. A lot of captive animals die from obesity, fatty liver disease, etc, and their metabolism at that age doesn't need that much food.
I'm so glad to hear it ended well, of course!