From Wikapedia:
"Each of us six officers had a shotgun and an automatic rifle (BAR) and pistols. We opened fire with the automatic rifles. They were emptied before the car got even with us. Then we used shotguns... There was smoke coming from the car, and it looked like it was on fire. After shooting the shotguns, we emptied the pistols at the car, which had passed us and ran into a ditch about 50
yards on down the road. It almost turned over. We kept shooting at the car even after it stopped. We weren't taking any chances."
[105]
The Browning Automatic Rifles (Monitor) were specially ordered for the possie.