I have not made any, but I have on my list to make a Gatling gun some day. I have looked at the carriage and wheels made by folks who have done this. A Cannon type wheel needs to be dished in order to look authentic. The entire carriage and attachments is a great woodworking project. In the pictures you can see the sections of the wheels and how the effect is real, a solid round outside with dowel type spokes just would not make a model look great. Look these over ( none are mine), they are just woodworking projects. The actual cannon is just a small part of the model. I included an example of a spoke, no dimensions because it is from a proprietary drawing for the Gatlin Gun, but it will give you the idea of how the wheel is dished.
Bob
--------------------------------------------------------------Dished Out Wheel---------------------------------------------------------------------------------------------Wheel Segments, Spokes not round
----- Here is real dished view------------------------------------------------------------------------------------------------------------------------------------------The wheel on this is about 15"
Bob
--------------------------------------------------------------Dished Out Wheel---------------------------------------------------------------------------------------------Wheel Segments, Spokes not round
----- Here is real dished view------------------------------------------------------------------------------------------------------------------------------------------The wheel on this is about 15"