Introduced: circa 1970
Straight from the "you've got to be kidding me" department, these brass versions of the Bachmann F9 and GP40 consist of Cal-Scale brass shells (made using the original Bachmann masters) mounted atop standard Bachmann F9 and GP40 mechanisms. Advertised in model railroading magazines during the early 1970s, these were sold exclusively by Gem Models (which I'm told was somehow affiliated with both Bachmann and E&H Hobbies in Philadelphia). Production on the GP40 was extremely limited (with perhaps as few as 15-25 ever having been made). The F9 models are much more common, with production purportedly consisting of more than 100 units. Both models were ultimately discontinued due to the high cost of producing the brass shells.
As noted above, these models employ the same Bachmann mechanisms that were used on the plastic shell versions -
Although fairly primitive by modern standards, these trainset-style mechanisms do run around in circles pretty well. Unfortunately, Bachmann's early 1970s gearing scheme (metal, metal and more metal) makes for just a whole lot of noise. So, interesting models for the collector shelf, but not really anything anyone would want to actually run on a model railroad.