I didn't have the shell selected, and it was centered around the Y axis. Anyways, I think I got it to work for now--I just hid all but a very small portion of the shell so that the repeats wouldn't appear. The images are still a little warped but it will do for now. Thanks for the help.
Also, shotgun shells have a very fine ridge-like texture all the way around the casing. Any ideas on how I could simulate that? If the shell was standing on end, the ridges would run top to bottom on the plastic part, and they are very small.