Just an idea - don't know if you'll want to take this sort of angle, but look at the AWB as a 5th Amendment and Lanham Act problem for certain manufacturers. Certain specifically named brands/types (AR15 for example) are trademarked. Now, while a trademark is not a 'property' per se, a valid mark can be a very valuable commodity. Companies like Harley Davidson pour hundreds of thousands of dollars into protection and maintenance of their marks, and those marks generate hundreds of thousands (if not millions) of dollars in revenue.
Its been a while since I've read Penn Arms/Navegar, but as I recall, the court denied their challenge basicly because (according to the court) it wasn't a bill of attainder because they could continue doing business, just not making the same guns with the preban features after the ban. As far as I know, Penn & Navegar (or anyone else like Colt) never made the argument that by banning future production of specifically named models, the government took a valuable commodity (the trademarked names and business goodwill associated with those trademarks) for a public purpose with out compensation in violation of the Takings clause.