Will a potato gun shoot rocks? Here's the thing ... EC told her friend in TN that CL was taking her shooting (in JTNP). Suppose he was taking her to teach her how to shoot a potato gun, or just out for fun shooting a potato gun. Then it wouldn't matter how long it took to reload or whether it always worked, and "point blank range" would do for a perfect shot. She'd be watching him load it, how fast could he pull it up/point/shoot? If she was just knocked down by it and otherwise not seriously injured, he could always say it went off by accident as he was about to hand it to her. Surely he could hit her hard enough with a potato to knock her out ... and if those guns will shoot rocks, there you go.
Since potato guns are generally homemade, there is no set answer for some of these questions, but that are good questions. Yes, a potato gun could shoot a rock. Basically, it will should anything that fills the barrel enough so that when the trigger (valve) is used, there is enough propellent behind it to shoot the object. Diameters vary, as do speeds, accuracy, length of barrels, types of valves and propellents. Without seeing it, we just have no way of knowing how long it would take to load or pull up and shoot.