What is a good path for somebody who desires to be a small arms weapon designer?

Question

People such as John Moses Browning, John Garand, Mikail Kalashnikov, and Eugene Stoner?

Answer 1

Mechanical engineering.  Most small arms use only mechanical components.

Answer 2

Start by enlisting in the military.  (Army or Marines)  This will provide real-world insight on how the products are used.  You will gain experience that you can draw upon when designing weapons in the future.  It also helps establish some credibility with your future customers.

Then get some experience with machine tooling so you can understand the manufacturing steps needed to make the weapons.

Get a part time job at a local gunsmith.

Answer 3

Mechanical Engineering, I second that.