This from the thread on Ammo Return
Before I started reloading I used Winchester 150gr pretty much exclusively in my .308. However, I've found when reloading that the Winchester cases are lacking neck tension, so much so that in a good proportion of the assembled rounds I can pull the bullets out by hand Other brass (Lapua, Norma, etc.) processed through exactly the same dies seem fine.
I only neck-size my reloads, so was trying to work out why only the Winchester brass would be causing this problem. I presume it is the brass thickness at the neck that is the cause of the issue? i.e. although the external diameter of the brass is the same, because of thinner cases the internal diameter on the Winchester brass is fractionally bigger. I was surprised that the difference between Winchester and the other makes was so significant.
I now have a lot of Winchester .308 brass that is cleaned and primed, but won't be used