To me, they're arranged in a straight line. The article (maybe I should have mentioned this earlier) discusses "Forced Feeding" of ammunition belts using an electric booster, developed by the
Hughes Aircraft Company Culver City California. I'm thinking the correct orientation of the photo should be thus...
Just a thought.
Is it possible that all the photos supplied to Popular Mechanics were from Hughes? Therefore is it possible that we're looking at a VERY rare photo of the "proposed" rear nacelle armament for Hughes' D-2...?