A bullet trap with a passageway defined between flat upper and lower boundary walls extending convergingly, at opposite angles of inclination of between 0.degree. and about 15.degree. to the horizontal, from an entrance opening to an exit opening or throat, and a deceleration chamber having a generally spirally curved circumferential boundary wall and provided in its upper region with an inlet opening and in its lower region with a discharge opening leading to a collecting vessel. The circumferential boundary wall of the chamber is constituted by two oppositely concave channel-shaped members the respective upper end regions of which are spaced from each other to define the inlet opening, and the respective lower end regions of which are spaced from each other to define the discharge opening. The chamber communicates at its upper region with the passageway substantially tangentially of the chamber via the directly adjacent inlet opening and throat, and a liquid lubricating fluid can be directed into the chamber from the collecting vessel either in a forced flow mode (pump-activated) through the inlet opening or in a passive mode (bullet-activated) through the discharge opening. For the special purpose of enabling a previously fired firearm to be checked for whether a bullet remains in the firing chamber of the firearm, the trap may have the same basic construction but without the liquid lubricating fluid feature.