This is an 1875 Holland being spoken about here so steel shot is pretty well out anyway. Some one may be tempted to try it though because of the cyl, cyl choking, but there remains the pressure thing.
Steel shot in a jug choke is not a thing I would like to do to any gun. The way I see it, the shot would likely shift out into the jug & then try to recompress to original bore size. The thing with steel is that it does not compress. There would be a pressure spike & possible split muzzle or wicked rivelling at the least.
O.M