acting without a clear goal; shooting in the dark
Idiomatic expression describing aimless action or effort without a defined objective. The literal image is 'a rifle in the dark'.
Starting without a plan is like shooting in the dark.
His approach is exactly like firing blindly; there's no telling if it will yield results.
手探り refers to doing something by feel or trial and error, often with physical or metaphorical groping, whereas 闇に鉄砲 is more about firing off actions without aiming.
Literally 'a rifle in the dark', this idiom evokes the image of shooting without being able to see the target, metaphorically extended to any aimless action.