If you are using brass fired in one rifle neck sizing is not the way to go as you found out. I know this is the obvious but in a situation where one chamber may be larger at the shoulder junction than the one in the next rifle, some dies are too large to resize brass enough for the other chamber. I have seen this several times before. The tell tale is a real shinny spot on the shoulder when resizing with a proper sized die. Lee dies for one will always size you case to fit a smaller chamber after brass has been fired in a different rifle.