I suppose some of the design came unconsciously from the new Halo Infinite shotgun which is also rumored to be semi-automatic as well. Though in truth I was brainstorming a design for a shotgun with a loading gate on the side of the body instead of the bottom, so this is the design I came up with today with the tube located over the barrel. The roughly L-shaped bolt travels backwards and moves a shell from the magazine into the chamber. The ejection port on the other hand is lower than the loading gate, so it is not a symmetrical design.

A charging handle is located at the fore of the weapon that does not reciprocate with firing. Additionally, the shotgun has a last round hold-open where the user can hit a bolt catch under the loading gate to send a new round into the chamber. If the user desires, they can hand-load a shell into the chamber, giving it a +1 capacity.

The stock is three-position and moves along the buffer tube of the shotgun. A rail system allows for attachments on the top of the weapon, though it does not come with fixed iron-sights.

https://www.deviantart.com/chris000/art/C92-Semi-Auto-Shotgun-847983745