I am having a similar issue, though the magazine tube is factory-installed. To answer the above troubleshooting question, the shell loads into the chamber fine from the magazine when I press the shell release tab. This is also true when the magazine full, also. However, the problem occurs because I can't just cycle rounds into the chamber with manual operation of the bolt only. I have to click the release tab each time. I haven't fired it yet. Any suggestions are much appreciated. Thank you.