The late Colonel Jeff Cooper was once asked about backup weapons. He said a handgun backing up a rifle was like a destroyer filling in for a battleship.If you want more than one firearm, consider two different applications with some slop over or common ammunition . People have fiddled with multiple use fireams with both practical and impractical results. The various combinations like Drillings, Cape Guns, the Savage 24 for instance. Then there are multiple systems like the Thompson Contender or various sub caliber barrel inserts, variable shotgun chokes or specialised amunition that often enough doesn't always perform as advertised ( Glaser safety slugs.)In real life, what you effectively get are the equivelent in wieght, headache and bulk of two firearms anyway- hardly the philosophy behind your version of the old AR 7. Firearms are like our knives in argument, availability and use. It still comes down to the user and appreciation for what people in our past used as 'state of the art.'I imagine most people would freak at taking a Hawken .54 alone to Alaska- and remember very few people actually carried this limited production, premier rifle in it's day!