Sketching with pen didn't come easy at first, it is time consuming and requires patience.
Here is a progress shot
Drawing with ball point pen requires lot of patience, precision and careful ness while sketching apply little pressure when shading to attain a good texture. Before starting sketch your work piece with a pencil or light stroke to act as a guide when sketching.
Unlike pencil you cannot erase ball point pen which is why you need to be careful while applying your strokes. There are various kind of stroke/hatching. Each has its own function when sketching.
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From @shadowmancer