Simple military science line. Relatively cheap and easy to hand build in the early game. The ammo portion at the end is easily expandable for extra red mags, if/when needed.
45spm might be considered on the low side, but it gets the job done early and it is roughly the same length as my other science/production lines. It's easy enough to build this early and buffer vials in a chest when researching non-military science; that way, this will provide ample production through the mid game.
v3 - removed chests and simplified design.