If you were going to start a firearms manufacturing concern ...

[Sixsa]

I'd go work for Kalashnikov USA to make the AK12, and Dragunov SVD.

On my own, I'd make yet another double stack, striker fired, polymer framed handgun.

 

[BAJ475]

I would start with 2011 pistol frames. All of the advantages of a 1911 with much greater capacity.