What sort of test are you using to establish that the hardness of the metal is exactly the same each time?
With all due respect, show me any consumer-available process that will make the hardness of the metal exactly the same each time - including not annealing at all. Even the most advanced annealers will not be exactly the same, because case to case, the brass isn't exactly the same, day to day, the environmental parameters are not the same. etc. The goal is not to be exactly the same, but rather to reduce inconsistencies to a feasible minimum.
What I did:
- Used 750 degree Tempilaq to establish a baseline for the placement of the torches and time (longer than normal) to keep the cases in the flames.
- Additionally, visually noted where the color change occurred in the brass when the Tempilaq indicated the desired temp had been reached.
- The above two established a baseline time, placement, and visual cue.
- Used the combination of those three to improve consistency case to case to make up for the fact that exact placement in the flames, day-to-day temperature differences in the annealing room, and brass inconsistencies impact exactly how long to anneal something. By drawing out the time, you have more latitude to enable a manual method to get closer to the perfect time.
If I ever move to where I can flame anneal again, given that I don't anneal a crap-ton of cases at a time, I'll likely go back to this method. Why do I think it was more consistent? My SDs increased about 15% immediately after switching to induction annealing.
On the efficiency side, right now I anneal a case in roughly 3-4 seconds, depending on the caliber - this includes loading and unloading. I'd probably be in more of the 12-15 second range for my extended flame annealing. Over 100 cases, it's the difference between 300-400 seconds (5 - 6+ minutes) and 1200 - 1500 seconds (20 - 25 minutes). Not huge, but significant enough to be a consideration.
Also, there is something oddly relaxing about manually flame annealing.