I have an Fie Miami Mod E 15. There is a spring loaded lock that holds the shaft that the magazine revolves around. The shaft has never popped out while firing. I received this gun in a unusual way and I have not fired it very often. It seems to be rather worn out, and gets hung up when fired. It is possible the your gun is worn too, or the locking pin is missing or worn. FIE went out of business, I am told, in 1990. Since I did not buy this gun and received it from a family member I don't have any history on it. I am looking for an assembly manual. I came to this site to try find one to download. I have found manuals for my other guns this way. My email is
cashbox@bellsouth.net if you find any additional information that can help me. Joe