Nice. I've never worked with molds before, but I do ceramics every semester at the local community college until I can afford a place in the country and a kiln and studio of my own.
Guess what the dark circular area is that can be seen inside the gun barrel http://www.sciforums.com/showthread.php?140914-Guess-what-it-is-or-ask-a-queston-!!!&p=3206862&viewfull=1#post3206862