New brass that hasn't been resized or had the case mouths work hardened from repeated belling or bullet crimping should already be in an annealed state, and further annealing is not necessary. Maybe contact Magtec for better info and advice.
The amount and the number of times the brass is worked determines when it is getting too brittle, and will then benefit from annealing.
Minimizing case sizing, neck expansion, and crimping will extend case life. I honestly don't know if annealing brass too often is a bad thing, and I'm a bit leery of a lot of internet advice from people who aren't metallurgists.
I can't guarantee it, but I've read that in general, annealing every 5-6 reloadings is good. And if you start seeing case mouth cracks, etc. then the intetval should be shorter. If you were lucky, you might know a friendly metallurgist who could test and track increasing hardness through successive reloadings on one or two cases to determine a good interval for your rifle and reloading operation. Paying to have that done might be more costly than replacing old brass.
