A good die can be made from your reamer/chamber dimensions. This is custom, it's good, but not fitted, which is better.
You don't always need the chamber reamer, or reamer print, while providing properly fire formed cases. Some custom die makers build the die to size down from that provided baseline. With this, you can steer the outcome to your desired sizing actions.
For a 6.5wssm imp wildcat, I wanted a bump die. This, for bumping of 35deg shoulders, with zero body or neck sizing.
I knew my die maker would build a body-bushing die to size down all provided as fire formed, by 1thou (after spring back). I did not want this, so I fire formed 5 cases to overpressure dimensions (+1-1.5thou), and sent these. With this, my die was made to squeeze case bodies during bumping -without actually sizing. I left the neck bushing out of the die, and this is how I ended up with my custom bump die, doing exactly what I want.
I have had bullet seating dies made with my finish reamers. Wilson die blanks, basically chambered like my barrels. Works good.
Before ordering a custom die, you need to know what you want and see that through. Otherwise it's not a custom die. It's just an aftermarket die, which might not be any better than off the shelf dies from other makers.
