To answer your question, the magazine tube appears to be held in place only by the friction of the full-length forend and the clamping effect of the top barrel band. If it comes loose, it makes for a frustrating feeding failure until you figure out what is going on. I had this problem with a(n) Uberti replica musket. The Uberti forend was very generously inletted for the magazine tube, leaving only the top band to hold it in place. I used a Brownell's bedding kit and did a sloppy glass bedding job on the forend, and that seems to have cured the problem. It's important to keep the front band tight, however.