I got a new batch of 100 Remington 300RUM brass. So I decided to check the neck thickness and sort by uniform batches. Holy cow. Some varied by .006". Most all were greater than .003". Thats a bunch of crap. So here I got getting busy and turned the neck to take off the high spots. Well all this neck working and use of expander dies causes the neck runout to be pretty bad and by the looks of it, they were bad from the start. So I picked out the worst one with .007" neck runout that has a uniform neck thickness now of <.001", and pushed it thru my Full Length die. It corrected the neck runout down to .004" from .007".

How much can Full length sizer correct for? I think the die is straight. I have checked several times with out expander balls from fireformed brass.

I figured the only way for me to have dead straight brass is to now fireform. I know my chamber is dead straight. I have checked neck runout after fireing hefty rounds and neck runout <.001". Whats the best way to fireform these badboys without loading up expensive bullets? I was reading you can use Unique and dacron, but don't know if I like that dacron burnt in my barrel. I thought about pushing 150gr Coreloks thru it.

Any help would be appreciated.

By the way, I checked the thickness of the neck of my federal 308 brass that has been once fired. Guess what? None were greater than .003".

That much variance in thickness in even the 308 prompts me to ask you how your measuring it?

Also have the necks been chamfered on the inside and outside? Do they have dents on them from something?

I have a sinclair neck thickness mandrell. First these cases are ran thru a expander die to make sure the neck is round. What does yours read? How do you measure it?

After talking to the techs at sinclair a few min ago, they said there is no way a FL die can correct for .007" runout. Only way to totally correct is to fireform. And nothing unusual about that runout of new Remington brass.

I use rem 300 wby brass because of price. I can't say that I've sat down and measured neck thickness variations but that sounds like way more than I would expect. The first thing I do is use my neck turning expander to slightly oversize the brass. I do an inside chamfer to remove any inside burrs. I then turn all the necks and then resize.
I can't exactly remember how good my runnout out is after this but I would expect a good percentage to be under .003".
If I was to use this brass as hunting brass I'd load up about 30 rounds for a trip. I'd mark the primers on those over .005" for foulers and general sight in. Anything under .003" loaded would get a green mark on the primer meaning to me "match grade". Off I'd go hunting chambering and using the 6-10 match grade I'd expect out of 30 rounds.
So what I'm saying is I feel I'd get perfectly good usefulness out of non fireformed brass--even for an expensive or fancy hunt.

I'd save the fired brass and resize. I almost ALWAYS get .0015" and under loaded rounds out of my rem brass in my "tuned" forester dies. BUT remember these are weatherby rifles with freebore and all that fancy runnout probably means nothing to the overall accuracy picture. You might also reload some of the above batch that was fired for final site in and use them for ammo to fall back on during the hunt.
I do like to make as good of ammo as possible but feel a few brass will always load up a little crooked and they can still be used for the prehunt prep. Just what works for me.

One other hint that's worked good for me on trying to straighten brass that has a bad attitude is to lube them good inside and out. Run them through the sizing die, rotate the brass 180 degrees and run them through again. If you have a die known to make excellent runnout I think you will see some good results.