I have had dies built both ways, through the use of a re-size reamer which the gunsmith used on soft die blanks & then the finished chambered die was sent to Fireball in Mass. for heat-treat as well have had several sets done through providing 3 fired cases to a custom die manufacturer. - My take is the easiest and less "risky" is to send 3 or 4 well formed pieces of brass to a reputable die maker such as Whiddens Gunworks or Warner Tool. (Warner Tool will cost more & take longer but the quality is second to none).
The "risks" associated with going the resizer reamer route can include: re-size reamer not ground to precise specified dimensions specified, wrong dimensions being provided for a re-size reamer for a particular cartridge, and then there is heat treat where things can not go as desired and the chamber cut in the die changes during heat treat process, and this throws the usability of the die out the window. - Another consideration is the costs involved, sending 3 or 4 well formed cases to a good die maker and paying the price they charge is more cost effective and cheaper than purchasing a re-size reamer, die blanks, paying the gunsmith to chamber & then the cost of heat treating. - And if it doesn't work out, then what ? - And who's going to "eat the costs" to correct the problem or out of tolerance die ? - The customer more than likely is my guess.
- The 2 sets of dies that I have that are made off of a re-size reamer are excellent, they size brass to perfect dimensions and fit for the chambers cut in the barrels that were cut by the finisher reamer, and heat treat didn't throw the dimensions out of whack. (fortunately)
- The cost was substantially more to do it using the re-size reamer method and one of the reasons that I went that route was the dies needed to be done on 1 1/2" x 12 die blanks and finding a die maker back at that time to send 3 or 4 fired cases to & have them build the dies I wanted (on 1 1/2" x 12 tpi) blanks was pretty much non-existent (2007).
Both Warner Tool and Whiddens can & will produce some very high quality & precision dies for most calibers if provided correctly fired brass to work with.
That's my .02
- Ron -