The only problem I ever had with keyholing was from a Ruger single action 357M. If I recall correctly, I used 158 lead bullets and a fairly stiff charge of Unique. My thought is that the bullets (locally made) were too soft and were stripping in the rifling, not spinning correctly.
Someone argue with me if required, but the only reason for bullets "tumbling" in flight is instability due to lack of spin. Yes? No?