On the consistent neck tension, yes, absolutely, I think it matters quite a lot. But with my loading practices - tight neck chambers, neck turned brass, bushings and never an expander, maintaining seems to be automatic. My necks have just a little over .001 total clearance in their chambers and get sized only about .002 after firing. And not the whole neck, either. I always leave some of it unsized. Depending on how deep the bullets are actually being seated, as much as half of it unsized. And never use an expander. The necks just don't get worked much at all.
I did do some experimentation years ago, with my most accurate rifle. It showed no improvement with annealing. All my less accurate "varmint" rifles (which are all custom barrels and tight necks), have the same neck clearances and sizing done to them. So, either the neck tension uniformity is not improved measurably by annealing for them, or, that improvement is not enough to show up in accuracy. For my rifles. And the way I load them. YMMV!
The thing I often hear is avoiding split necks. But I never have split necks. Ever. Indeed, when I do anneal very well used brass, it's because the shoulders have become difficult to bump and to need it more frequently.
And no, I don't believe anyone can match the consistency and precision of a machine, either.
But, what are the tolerances? I don't know. But I'm not sure that the acceptable tolerances for a "proper" annealing aren't within the capability of a reasonably careful human operator? People have been doing it for a very, very long time before these machines became available.
I do know, you can get them too hot, obviously. I don't go for any glow of red at all, myself. I think if you can see it glowing, it's too hot already or close to it. The brief use of Tempilaq made that clear. I go by shoulder discoloration. Which might take a few seconds or more to happen, but when it does happen it's all at once and at that point I remove it from the heat. They end up looking as consistent in that discoloration as new Lapua does. As mentioned earlier, I did experiment with Tempilaq, but found it turned at the precise moment the shoulder discoloration occurred. And it was a PITA to get off. And the shoulder discoloration was actually easier to see and more of an abrupt signal.
Eyeballing it like that is plenty good enough for my only occasional need.
No issues with using a machine, or even paying someone else to use one though. If I had a machine given to me, I'd use it.
I just question how precise the operation actually needs to be? And whether a plain old human can't really perform it within the acceptable range of temperature and time. I really don't know. But, like I said, I'm satisfied with the results I get.
- DAA