Regardless of how things 'Used' to be done,
This is the 21st century, science marches on...
Mr. Guffey's impenetrable posts aside,
OBJECTIVE: To impart enough energy to the 'Brass' alloy the molecular structure,
To a point the 'Brass' alloy molecules space themselves & realign.
OBJECTIVE: To NOT over heat the brass to the point the alloy separates into base metal components and looses the properties we value in cartridge brass.
1. Energy Application To Excite Molecular Movement/Realignment (spacing) restoring properties benifical to said 'Brass' (non-ferrous metal alloy),
Imparting energy ONE of TWO ways...
OUTSIDE heat source (flame or heated object), that requires a substantial TIME for the THERMAL ENERGY (heat) to saturate the alloy throughly,
OR,
Magnetic Induction causing the actual molicules of the alloy to create their own 'Heat' through friction with each other.
TIME is substantially reduced with magnetic induction since ALL molicules heat at the same time & at the same rate,
The ADDED benifit of magnetic induction exciting at a molecular level isn't reaching the target temperature,
But the nearly perfect spacing of the molecular grain since every molicule spaces exactly the same when moving.
The 'Brass' alloy literally grain spaces & aligns on a molecular level.
The issues with thermal dynamics (heat inductance & thermal 'soak') is reduced to milliseconds instead of minutes since the alloy restructures itself on a molecular level.
With External heating, there are thermal soak (induction/conduction) times to consider,
A fine line between NOT overheating the outside of the case, while waiting for the inside of the case to reach critical temperature target.
There is a consideration for NOT overheating the base of the case through heat soak (induction/transfer), if you actually believe modern firearms are ONLY viable when a 'Hardened' case is used...
The argument against this would be 'Proof Testing',
Depending on the 'Proof Test', some firearms will hold back anywhere from 30% overpressure to 200% overpressure,
Either way far exceeding the capacity of the case to 'Add Strength' to the chamber...
Two examples of this are civilian 'Factory' cases coming 'Dead Soft' from the manufacturer,
And military cases coming 'Half Soft' at the rim/extractor groove only.
I see the argument of 'Over Annealing' the sides of the case as a scare tactic at best for modern firearms, and at worst an 'Old Wives Tale' passed on out of ignorance.