Tony: Your M-8 Spare Barrel bag has an intresting background. M stand of course for Military. You may have heard of M-1, M-16' rifles, etc. The M-8 is a modern weapon and as such is a modular weapon, taking three different barrels for different functions. Most M-8s would look similar to the current M-4, with a shorter barrel than the M-16.
I realize this may be more information that you might want but never the less a story goes with your fly rod bag. Jonezee