When you are pushing the neck back it is a good idea to check for thickness or donuts at the neck shoulder juncture.
Reducing the neck from 30 to 284 shouldn't cause excessive thickening but moving the shoulder back can. A more severe example would be making 7x57mm or 250 brass out of 30-06 or WSM brass from 404 Jeffrey cases this can easily create thick necks or donuts.
The only batch of brass I have encountered that really needed neck turning was some early 270WSM brass. It looked like it was formed from Ultra mag brass. Fired cases were almost the same size as un-fired, not good especially when flirting with 65,000 psi.
"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli
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