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It cost me 10 minutes time with each one using a 1/4" wood dowel split at one end with 600 grit emery paper on it passed in and out of the die that was chucked up in a lathe. Any 'smith could do that, I hope.
One cause of case necks being more bent after bullet seating than before is the shape of the case mouth at its edge. After trimming, a ragged edge is left on the inside. Traditional deburring tools remove that one and put smaller ones at each new edge on that angled surface. It's the inside one that the problem. The smaller the case mouth is than the bullet diameter, that sharp edge puts resistance on bullets going into the case mouth. Too much resistance makes the thinner side of the case neck and shoulder give way and push back bending the case neck even more.
Solution? Make that inside edge on the case mouth rounder and smooth. After deburring with a conventional tool, put a No. 5 Easy Out in and turn it clockwise to debur that edge. Then run the case mouth over a bore brush spinning in a drill press; a few times back and forth will very nicely round that inside edge of the case mouth. Much less resistance hereafter and case necks retain their tiny angle to the case body axis. Sizing cases so their mouth diameter's a bit bigger helps, too.
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