Multiple Barrel Rocket Launcher (MBRL) systems are low-accuracy high-impact weapons meant to deliver barrages of explosive warheads across a wide area of attack. Due to their high mobility, firepower, relatively low cost, and ease of operation, MBLR systems are continuously deployed across conflict regions. High rates of failure of MBLR rockets on impact and their wide area of ballistic dispersion results in a long-term unexploded ordnance (UXO) concern across large areas where these systems have been deployed. We present a newly-developed and experimentally-tested aeromagnetic method to remotely detect and identify the most common MBRL-generated UXO - the unexploded 122mm rounds of the BM-21 MBLR. Specifically, we rely on rapid wide-area scanning by a UAV-based microfabricated magnetometer (MFAM) system mounted on a long-range hybrid-powered UAV platform. We tested a number of sensor configurations and calibrated the system for optimal signal-to noise data acquisition over varying site types and in varying environmental conditions. Finally, we developed a processing algorithm that allows near real-time analysis of magnetic datasets in the field and accurate identification of magnetic anomalies associated with both surfaced and buried BM-21 UXOs. This approach allows to rapidly assess wide areas and determine presence and orientation of unexploded BM-21 rounds, allowing to significantly constrain search areas for their subsequent removal or in-place destruction. Results of our field trials conclusively demonstrate that implementation of this geophysical system significantly reduces labor and time costs associated with technical assessment of UXO contamination in post-conflict regions.