When the 308 neck is necked down to .257, the thin spots will be made thicker, so the process will tend to make a uniform neck thickness.



But when the 6mm neck is expanded to .257, the thin spots will be weaker and stretch more, making them thinner. This will make thickness less uniform. Stretching too much may harden that spot and send the stretching elsewhere, but that part of the neck is then susceptible to cracking until annealed.



What does it all mean?

Buy the .257 pilot

Make the 25S popular.



--

A society that teaches evolution as fact will breed a generation of atheists that will destroy the society. It is Darwinian.

That would probably work but likely you should anneal before you use them as that much working of the neck will lead to early splits if you don't. The mandrels are cheap, why not just get one and do it right?

I tried it and it seems to work just fine. Then as an after though I went over to my layth and turned and polished a 25cal. stud. Took about 15 min., don't ask why I even thought about the other way.