Centered. The project in question is going to be an air cannon with a revolver-style drum. With each shot, the drum will rotate and bring up the next chamber (Filled with a nerf rocket or a paint grenade or a length of rope or whatever else I need/want to propel faster then I can throw). Speed, I'd like to be able to have them rotate in at most a second. Accuracy needs to be within a few degrees-whatever is in the chamber won't have to line up *perfectly* with the barrel every time, but the closer the better. (However, they'll likely be somewhat loose in the barrel, and probably with a degree of squishyness or in a sabot that will let them pass through minute differences in alignment between the barrel and the chamber).