I think the first guy to build these plain guns was Barney Schimmel. You can call a plain gun by his first or last name, whatever suits your style. Don Getz is a first name kind of guy.
There are some German guns with no metal furniture, so the buttplate, guard, sideplate, thimbles, etc, are all made of wood. But this is hardly a money or time saving trick, it is really a gunstocker's joke, and a way to show his/her skills. The buttplate is carved from the same piece as the stock, and is all faceted and engraved to replicate a metal plate.
