Trebonianus: http://www.roman-emperors.org/trebgall.htm
Trajan Decius: http://www.roman-emperors.org/decius.htm
Aemilian: http://www.roman-emperors.org/aemaem.htm
Here is an interesting characteristic of mid third century sestertii:
Look at the little metal flaps on these two sestertii (both Trebonianus). These flaps often occur on directly opposite sides, and usually are on the top and bottom of the obverse portrait. The lower picture shows coins with the flaps removed, leaving a 'razor edge.' I believe that flans were often produced in rows, connected at the top and bottom. The flan flaws we see here are the results of the flans being chopped apart. If the craftsman made a muck of the job and left a hanging piece of metal, he either hammered it back on to the flan (top picture) or chopped it off (below).
Volusian and Trebonianus with the razor edge flaw.
Some people have claimed that flans of this period were sawed off of a bronze rod. That doesn't make sense though; we never see saw marks in the fields, and sawing bronze rods with a modern hacksaw would be a miserable task, let alone using ancient saw technology. It would be most efficient to pour the molten bronze into as near flan-shape as possible and this is what was most certainly done.