He missed one important modification which I had done to my Double barrel which I use for early War pre 1862. The conversion to use musket percussion caps instead of pistol caps. This gives much better ignition and simplifies the supply problems of two different sized caps in the supply system of the company. I know officers carried pistols.
And yes many of the troops in the Trans Mississippi in 1862 were armed with shotguns after Van Dorn took everything he could lay his hands on to Mississippi. In August of 1862, prior to Arkansas Post, the entire armament for one Infantry Brigade was 20 shotguns and 2,000 round of ammuntion for the same.