The gun-type burner is an oil burner frequently used for industrial and domestic applications. The oil droplets are mixed with air and the flow generated is extremely complex and requires the combination of different techniques for its complete description. Here, for the first time, the full three-dimensional velocity vector map has been measured for different droplet sizes in non-reacting conditions using stereoscopic PIV together with a technique called multi-intensity layer, that allows size discrimination by accounting for differences in the scattered light intensity. Different spatial structures are detected depending on the droplet size: droplets under 30 µm in diameter follow the incoming airflow and entrain the recirculation zones while droplets bigger than 50 µm penetrate due to their large momentum. Differences are also found for the swirl component near the baffle plate, measuring stronger swirl for droplets smaller than 30 µm.