I've been mulling this around for some time and I've hit a wall.
I've been thinking about a custom powder through die (actually just the expander) for a Dillon 550B for 38 Special.
I was thinking about an expander profile similar to a Lyman M die or a RCBS Cowboy die that could be used for full wadcutters.
I want the expander to go deeper in the case to reduce the chance of the casing swaging the bullet down but I don't want to remove all of the neck tension. I also don't want to overwork the mouth of the casing where that M die type step is located.
Am I reinventing the wheel? Has someone done this already?