Putting an 800mm lens in a shoulder bag?

A few years ago, I was gifted a Billingham Hadley Pro shoulder bag. It’s a very well-made waterproof bag that is ideal for use as a walkabout bag for smaller kits. It’s dimensions are fairly small: 15 3/8″W x 6 3/8″ D x 9 3/8″ H. This makes the Hadley Pro an easy bag to put under an airplane seat as a personal item when traveling. I’ve taken this bag to places like Croatia and Scotland, where it was perfect for a small travel kit, like a Nikon Z7 ii and two zoom lenses.
However, I never thought I’d use this bag for transporting a super telephoto zoom. That is, until I tested it with my OM Systems OM-1 camera and Olympus 100-400mm f/5.0-6.3 lens, which has an equivalent angle of view to a 200-800mm lens on a 35mm format camera. By removing the lens collar (something I don’t need for hand-held shooting anyway), I was able to easily fit this telephoto zoom into the Hadley Pro bag. The OM-1 with 12-45mm f/4 lens attached fit as well, and I still had yet another empty compartment available to me.

My colleague, Rick Walker, pointed out something else while we were out shooting together. One could theoretically pair the 100-400mm with the outstanding Olympus 12-100mm f/4 zoom and have a two lens kit that covers the entire range from 24-800mm equivalent, in a bag that fits under the seat of an airplane. Mind blown!