Resizing brass, 308 to 260

[RyanG]

one more question.... is the same true if you neck up in size..... like say from 243? Just trying to wrap my head around this.... do the inside of the necks need to be trimmed too?

[yobuck]

factory chambers are as a rule sloppy enough that neck turning isnt necessary even when necking down cases.
even custom chambers can be cut so that neck turning isnt necessary. commonly referred to as a (no turn neck chamber).
turning is a pita that should be avoided unless your a serious competetor. a gunsmith could tell you what your neck dimensions are
by making a chamber cast. other than that im not sure there is another way of telling what the true dimensions are.
turning necks for the sake of turning necks can be counter productive and actually ruin brass as far as using it in standard dies.
trust me on that. loose primer pockets are as a rule caused by pressure. it would be unusual that it would occur after just 1 firing
unless it was an excessive ammount. id be double checking the load to make sure that wasent an issue. pressure can also show up
more in some brands of brass than with others. the pressure is there but some brass can handle it better. you usually get what you pay for.