I haven't found any information supporting Redbird or Samuel Sixkiller being in a 'Kansas Artillery company'. I did some searching to see if there was a connection with Hopkin's Battery -- the 4 guns captured from the Confederates at the Battle of Fort Wayne. Britton does not mention this connection in any of his books. It would be Britton's style to draw attention to "Indians" on artillery crews. It could be that they were supporting a battery as opposed to being on the gun crew.