Those are exceptionally nice pieces. I tried to make a loading block once but it didn't turn out particularly well. Is there anything special you're supposed to do to the underside of the holes so they line up well with the bore? That was a problem for me.
Holes smaller drill first writhe [10mm] and later expanded them gently with the help of mini grinders, often by checking the diameter with the ball.
After drilling the hole edges were ragged, but grinding to correct it.
This wood behave in an uncontrolled manner during drilling due to the lack of a single grain orientation...