Back in 2007/08 a company called Monolith Arms was promoting a pump-action 12 gauge shotgun they designed. The shotgun was notable because it fed from a horizontally mounted magazine inspired by the FN P90.  They shotgun was promised to be on sale in 2007, when they did not ship it in 2007 they promised it in 2008, but again it never materialized.

https://www.thefirearmblog.com/blog/2013/06/25/monolith-arms-p-12-p-90-like-shotgun/