Spider climb lets me climb walls and ceilings by making my hands and feet stick to surfaces.
The spell specifics from the Labryinth Lord Advanced Edition Companion
The subject can climb and travel on vertical surfaces or even traverse ceilings as well as a spider does. The affected creature must have its hands and feet free and bare to climb in this manner. Any objects weighing fewer than 5 pounds cling to the spell recipient's hands. No spells may be cast when under the effect of this spell. This spell may be used on another being (touch required) with no saving throw.
Can I load and loose a sling bullet while clinging to the ceiling, without falling?
I suspect the GM might rule I'd fall, but I might suggest that if I loaded the sling first, climbed to the ceiling with loaded sling in mouth, then I only need to let go with one hand to use it, three points of bare contact on the surface would remain. If I fall, the cinematic play and possible surprise might be worth the attempt.
So does this work in Labyrinth Lord.