Whats the best way to deal with the Doughnut?

[Rust]

Well after writing up a huge post full of numbers and measurements and theory and such to ask these questions..... and then deleting it all.

How should one go about dealing with the doughnut formed when necking 7.62x39 down to 6.5G
In my case if I size and don't expand I see a thicker portion (.250 by the shoulder vs .255 by the mouth) on the ID and a relatively consistent OD. Or if I expand the neck after sizing a relatively consistent ID and an OD of (.295 by the shoulder vs .290 at the mouth).
So do you ream out the unexpanded ID to .255 or turn down the expanded OD to .290 or does it matter?

Brass is KP (Lapua) and some totally unmarked brass. Both are quite consistent case to case with the unmarked brass being about .002 thicker in the neck dimensions than the KP. Also the thicker portion that I'm seeing is roughly half the length of the neck, not just a ring at the junction of the neck and shoulder which is what I had always thought was a classic "doughnut". My father in law told me that it was (is?) common for military brass to be formed with a thicker neck or thicker portion of the neck that sounds similar to what I'm seeing so maybe this is not a "doughnut" issue but simply one of case design.
Dies are Redding without the bushings. They do seem to be working the brass quite a bit, from my measurements some .010 difference between a case that has run though the die without the expander and one that's been expanded. Then thou's not much, but it seems that five would be plenty to get any of the cases I have down and then back up to size.
The FIL does have a Lyman neck turning set as well as a large collection of machinists reamers. (And a pile of metal to make a sanding rod if it comes to that) which I can snag from him next time we see them.

[rasp65]

Rust after fire-forming I re-sized the cases with the inside sizer button in place,then I turned the outside of the necks with a forster neck turning tool. I set the tool to do a cleanup of about 75% of the neck surface. Most of the material I removed was from the old shoulder neck junction to the bottom of the neck .

[Hoot]

The best approach is to order a custom Wilson inside neck reamer that just clears the inside of the neck, but catches the donut. Being cheap and impatient, what I did was take a piece of hardwood dowel that is straight and parallel and about one piece of 320 wet-or-dry thinner than the neck ID and using a dremel cutoff disk, cut a slit about an inch down one end (like tinker toys). I cut little strips of the wet-or-dry and anchor one end in the slit. I wrap it around the stick exactly one layer with no overlap. I chuck it in a variable speed drill and spin it down in the neck until it bites into the donut. A few seconds of rotation and the donut is effaced. The strip usually loads up with brass, so change strips each case. It took an hour or so getting all the dimensions worked out, but once done, it works great. You can get a lot of strips from an 8x10 sheet and if you have a paper cutter, you can crank out a hundred strips in a few minutes. It's initially tedious work, but you only have to do it once and your proficiency improves the more you do. It might cost you one of two cases getting it down pat. The most important aspect is having a decent inventory of junk boxes with dowel and rod stock to allow you to find the right one for the job. You can also use a piece of 1/4 inch aluminum or brass rod to accomplish the same thing. In my case, I stumbled upon the right piece of hardwood before I went to the metal rod stock box, so that's what I wound up using. If you find the 320 is too aggressive for the size of the donut, use 400, 500 or 600. It's a learn as you go thing...

Hoot

[pinzgauer]

How should one go about dealing with the doughnut formed when necking 7.62x39 down to 6.5G
In my case if I size and don't expand I see a thicker portion (.250 by the shoulder vs .255 by the mouth) on the ID and a relatively consistent OD. Or if I expand the neck after sizing a relatively consistent ID and an OD of (.295 by the shoulder vs .290 at the mouth).
So do you ream out the unexpanded ID to .255 or turn down the expanded OD to .290 or does it matter?

Curious what dies you are using??? I ask because I shoot nearly all IMI 7.62x39 brass, and have never had the donut issue, nor has my brother.

The Forster dies seem to size less on the OD, but about the same on the expander. So they work well on thicker case necks (IMI fireform), OK on Hornady, and do not size down enough for wolf/ppu.

So I'm wondering if by working the brass less it's dodging the donut issue?

[Rust]

Info being added to original post.