It seems we have focused on the load as being the culprit
in the keyhole issue - which it could be. But - - - -have we considered shooter technique?

Many years back while shooting BE, one of the military shooters did a demonstration on keyholing by using heel pressure on the grip at the time of trigger let off. Could make the bullet keyhole right or left and call the direction of the keyhole depending on heel pressure.

Just a thought