Impact-pulled bullets can shoot weird even with something soft in the bottom of the puller to keep them from being deformed. Before they even leave the case, the cores of cup-and-core bullets can be loosened slightly. You'll never notice any difference in appearance, but some will be unbalanced.
This can't happen to bonded or mono bullets, but it definitely does to cup-and-cores--and you can't tell from looking at them which ones are loose.
