Roscoe Regulator

My gun needs .430 bullets, so I do well with the RCBS Cowboy dies (need to lube cases). The bullets are shared with 44 Special. The issues I had with chambering or gauging were solved by trimming cases. I would say that picking a die will require an awareness of bullet diameter. The .427-.428 bullets probably would not fare well with the Cowboy dies. It depends what you mean by 44-40, by the book or the actual gun in hand. Mine is a Uberti Outlaw with throats that allow a .430 bullet to pass with mild coaxing.