Have you tried taking the men out of the slots before you move the gun? I've heard that can help, but don't remember if I've actually ever tried it.
Perhaps someone who is more familiar with the .upc files could offer a suggestion, too.
Edit : See the following
http://www.subsim.com/radioroom/showthread.php?t=136620
http://www.subsim.com/radioroom/show...748#post899748