Well, John M. Browning and his brother used to carve out wooden models of all their rifle action designs, part-by-part, and when they had a complete working wooden model with ALL THE BUGS WORKED OUT, they'd reproduce it in steel and take it to the major arms companies to see if they could interest anyone in making it!

You could do the same. But in this day & age, there are few new ideas. So to be successful, your designs would have to be original, offer a distinct advantage over every design now being made, and be economical to produce. These days, no company would be interested in producing a design that is labor-intensive!