The Langnickel Royal Sable Brushes have been discontinued by the manufacturer, and we none left. Traditionally, oil painters have used hog bristle brushes because of their stiffness - important in pushing paint around.  However, the bristles are thick, and make it a challenge to control lines and details.  Synthetic brushes can have much thinner bristles, and therefore offer much more control over detail - sometimes too much, eliminating randomness.  One unusual brush, used by many painters, was this Langnickel Royal Sable. It had a certain springiness while keeping a soft randomness so the strokes are free - and you can see the brush lines.  This is not Kolinski Sable or Red Sable, both soft but very controllable, but is actually mongoose hair.  Supposedly this brush was used by such painters as Richard Schmid, Jeremy Lipking, Dan Gerhartz, Morgan Weistling and others. If you look at their style of painting you can see how wonderful the free brush stokes look.