Observation of current-carrying plasma arcs driving solid projectiles in round-bore and square-bore railguns have been made with magnetic induction coils. Both free-running precursor arcs as well as projectile armature arcs are observed. Qualitative behavior of the plasmas is inferred from data and compared to basic physical models. The non-uniform nature of the force on the armature is investigated. Experimental details as well as difficulties in calibration and in quantitative analysis of magnetic probe signals are discussed. Evidence suggesting evolution in the structure of free-running arcs is presented.