I have two cases for my QCB, the I Shot and a Pelican. The Pelican is the smaller case, that I can put the QCB in pistol configuration on the top, with all of my barrels and bolts and optic in the bottom. It is great for maximum protection.
I just started using the I Shot, and love it. With all of the webbing inside, I can get the completed rifle of any configuration in the main compartment with a lot of accessories, and all of the webbing in the outter compartment can hold several barrels and "stuff'. With my upper, lower scope red dot and four barrel/bolt combos, so far it is pretty heavy. The bag is hell built for stout, and carries everything quite well. I have a Tan 42 inch case, and it is tall enough to fit the completed rifle with a 30 round magazine, and a Nightforce 3.5x15 by 50 with the tall knobs.
What I am doing with my spare barrels is using one of the gun sleeve type socks to put the barrel in. I then use velcro loops that I made (additional to the one you can buy) to hold the barrels parallel to the long length of the internal webbing on the outside compartment. I use the shorter socks for the scope when it is off the gun or on my Aimpoint. Everything stays put very well, and the tan case does not scream gun. The plastic dividers between the foam help keep everything in place, and nothing prints.
I am very pleased with the system, so far. Although a couple more barrels and bolts (which are on the way), and I might need a back brace to move it around
Craig