It is synthetic as is the bulk of the stock except for the steel, molded in rubber butt plate. for me I would give it a "high" durability rating, but with that said, these are hardly the rifles I would "test" that rating with any form of abuse. You bring up a good point about the size of the tube itself. I've never measured it, so I don't know if it is Mil-Spec, or the larger commercial size. Bill T.