I wonder if they had changes during production, because I'm pretty sure the one I had would fire in single or double action. I never opened up the frame though.
There were a couple I rebuilt, that I also modified for single action. But single action was kind of useless, as the ball sitting in the breech (lifting block), would just roll out the barrel if the gun was pointed anywhere near down (no ball detent of any kind).
Empire AXE / Invert Mini / Empire BT TM15 / Tiberius T8 / Eagle 68 Pistol
Crosman 3357 Revolver / Mark V50 Revolver / AGA62 Pistol / Nelspot 007