I was able to handle the SRM Arms semi-automatic Model 1216 shotgun at 2012 SHOT Show. (Please note that you can click here for the latest news from the SHOT Show.) One of the interesting features of this particular scattergun is the revolving high capacity magazine. Instead of a single magazine tube, the SRM 1216 has four tubes that quadruple the amount ammunition loaded.
Changing magazine tubes is accomplished by flipping a simple thumb lever located on each side of the front of the magazine. This releases the action and the entire tube assembly is rotated by the operator.
I tried rotating the magazine tubes and found it to be very intuitive. It is obviously much faster than stoking a regular tube full of loose shotgun shells to up your ammo.