Siacci was briefly part of the campaign against the Austrians in a war in 1866, until he was sent back to Turin to teach ballistics at the Military Academy.

A year later, he was promoted to Professor of Ballistics at the School of Applied Artillery and Engineering in Turin and held that post until his retirement from the army as a major general in 1892.

Siacci is well known for his contributions in the field of ballistics, distinguishing himself with a famous treatise Balistica, published in 1888 and translated to French in 1891.

Of great importance is an approximation method he devised to calculate bullet trajectories of small departure angles.

Siacci's theorem in dynamics is the resolution of the acceleration vector of a particle into radial and tangential components, which are generally not perpendicular to one another.