There are 28 gauge shotguns in use today, but they mostly are the side/side or over/under crowd (think Beretta, Purdey or Holland & Holland). I've only seen 28 gauge chambered in break-open guns; never in pump or auto...
29 gauge was someone that didn't know what they were talking about.
At one point in time, there were "commercial" grade shotguns in the 10, 8, 6 and 4 gauge varieties, as well as a few other "offshoot" chamber sizes. These were typically mounted on boats or wagons and were the equivalent of having a 20mm flak gun dialed in for zero altitude. Commercial hunters of 70-100 years ago used these on geese and ducks. The amount of shot and powder these rounds held made it easier to reach higher and take out a wider swath of birds...
You certainly didn't see one putting a 4 gauge to their shoulder.
