I got some Lapua .220Russian brass a while back to form into 6PPC. I sized and loaded it with some cheap bullets to fireform. 1st problem; won't chamber, the neck diameter is larger due to a thicker neck.
SO I ordered a neck turning tool. Bout time too, I was looking for an excuse.
The brass lay loaded till I could be bothered just now to pull the bullets and started prepping it properly.

Question and note(my caliper is broken now, so I don't have any real measurments):

Can I load a Lapua case with a bullet, take the neck measurment, then the Sako brass neck with the same bullet loaded, then shave off the difference (or just less than for a tighter fit?) on the Lapua cases that have now had the pullet pulled??

I assume that the neck will "spring" back a bit tighter that it would be with a bullet loaded due to the tension, but what difference should that make?

After that I should be ok to fireform, right?
I am apprehansive because I get the feeling it would be best to form with wax plugs and pistol powder first, then turn the necks.

I hope that's clear, I got myself confused writing it...
Atucally, I'd have to shave off half the difference since it would come from all the way round the case...

What size is the chamber neck measurment? The diameter of the loaded round should be ~.003" under chamber size in a hunting or varmit rifle to insure enough room for the case to expand and release the bullet. Benchrest shooters go down to even less clearance between the case and chamber but in the field this can lead to problems.
The case may just need a few thousanths removed to "clean them up" and then again you may have remove considerable material. You idea to copy the neck measurment of a loaded factory round should get you in the ball park but you may be takeing more the you need off depending on the chamber. If you`ve a case that`s been fired with a stout load and is still unsized try turning your cases until the loaded round copies the fired/expanded neck measurement, this should be closer to where you want to be.

I don't give any more room than .002" clearance total. Second,..if you are going to do it right, you need to buy the neck thickness micrometer. I have the sinclair version and it is very accurate and easy to use.

http://www.benchrest.com/forums/ (Centerfire Benchrest)Great info there, do a search. Or on this site, go to benchrest & target shooting.

I generally make my first neck turn before necking and fireforming, just a hair off the top to clean up any high spots and thin the neck just enough to chamber after necking operations (.0015" clearance, minimum). Final cuts are made after fireforming.

A ball tube micrometer works wonderfully to tell you exactly where you're at.

That's just the way I do it.

I just had a similar experience with one of my wild cats when loading larger than calber gas checked bullets for the first time.

I pulled the bullets and tried to chamber the cases. They wouldn't.

I knew I had to remove at least .004" off the diameter(.002" radius). I brought the cuting tool down till it just hit the largest diameter on the neck and than backed the tool off the neck so it no longer touched the brass.

I moved the set screw in just less than 1/12 a turn or almost 1/2 of a flat on the allen wrench.And made my first pass.

The case than chambered. I seated a bullet to see if it would than chamber and it did.

If yours does not, repeat the process but move the cutter in a little less.

A full turn on the set screw will be between .025" to.031" on the RADIUS. The allen wrench has 6 flats. The rotation of one flat than = between .004" to .005" ON THE RADIUS roughly.This is simple and in this case you won't need a micrometer or caliper but you will eventually. If you have any questions PM me and we can talk on the phone. roger

So,Aussie! What did you do, besides teaching the ladies about wallaby meat balls? roger

iF THE NECK DIA. IS NOT KNOWN, A CHAMBER CAST IS A GOOD WAY TO FIND IT OUT. IF THE NECK IS A .262 AS A LOT OF THEM ARE, IT IS NECESSARY TO TURN THE CASE BEFORE TRYING TO FIREFORM IT. YOU CAN GET A VERY GOOD IDEA OF THE AMOUNT OF BRASS TO REMOVE BY SUBTRACTING BULLET DIAMETER FROM THE NECK DIAMETER AND DIVIDE THE REMAINDER BY TWO. SUBTRACT TWICE THE AMOUNT THAT YOU WANT FOR CLEARENCE AND YOU SHOULD HAVE THE THICKNESS OF THE NECK THAT YOU WANT. IN MY OPINION YOU REALLY MUST HAVE A TUBING MICROMETER TO GET THE NECK DIAMETER CLOSE ENOUGH. PLEASE EXCUSE THE CAPS. AS I WAS ALMOST DONE TYPING BEFORE I NOTICED IT.