Best time to neck turn, and eliminating donuts

[HodgdonExtreme]

I'm working with a 308 parent 7mm wildcat that pushes the shoulder back a little while sharpening up the shoulder.

Beginning with Winchester head stamp 243 brass, I formed the cases, necked up with a Sinclair expander, and loaded them. The bullet is seated so the bottom of the bearing surface is right at the neck/shoulder junction. My chamber's neck is .317", and measuring a loaded cartridge, the neck measured ~.310", all the way down the neck.

Much to my surprise, 7mm08 starting loads (very similar case capacity) showed wild pressure. Backing way off and working back up, I found ~42.5gr H4350 @ ~2500fps to be max safe.

This didn't sit right with me. I repeated the test starting with RP 260 brass, which performed about as I expected - 45.5gr H4350 + 175smk = ~2725fps.

I assume the winchester brass has donuts - but I can't measure them?? I thought, if there was a donut, I'd be able to measure the neck get fatter on a loaded cartridge just above the shoulder....??

Revisiting the winchester brass, I tried neck turning 2 ways:

First, I sized back down to 6.5mm, then K&M expanded to 7mm - but leaving the very bottom of the neck unexpanded. Then neck turned using the carbide cutting pilot. The inside cutter removed a bunch of material inside the bottom of the neck, while the outside cutter skimmed only a liitle, and didn't skim at all towards the bottom.

The second batch got fully expanded via K&M mandrel, then turned. This time the inside cutter did nothing and the outside cutter skimmed the neck until it reached the bottom of the neck, where it removed a good bit of material.

Then I did load work ups with both batches, and neither showed early pressure. Both methods seemed to work.

What's the best way to do this moving forward? Why couldn't I measure a donut, when there must've been one?

Thanks in advance for any insight.

 

[shoot4fun]

When I had a BR gun in 6ppc I would neck up 220 Russian with an 6mm expander die first. Then I turned the outside neck diameter to .260 (.262 neck chamber) and let the neck turning tool cut down just below the junction of the neck and shoulder. When fire formed the case body was blown out and there was no donut. I was always told by the guys who had done it a lot that the key to good cases with no donuts was turning down on the shoulder just that little bit.
Jump ahead to when I decided I wanted to use Lapua 260 cases for my 7MM08. I originally tested with R-P 260 brass and was able to get clean necks without donuts or case trimming. I thought it was going to be just that easy but the Lapua brass threw me a curve; it had thicker case necks and would require trimming. So, thinking back to the PPC, I turned the necks down past the neck-shoulder junction and fire formed brass that has no donuts.
I have always done the neck turn step before the cases are fired in the chamber. Same with when I shot a 6 Dasher with a tight neck. There I formed a false shoulder just where the bolt would close on an unfired 6BR case that had been necked up first to 264 then down (partially) to 6MM. Neck turning was performed and then the cases were fire formed.
Not sure any of this is what you are looking for but hope it helps.

 

[jsthntn247]

Next time neck down instead of up and you won't get donuts. Use .308 brass and a false shoulder.

 

[HodgdonExtreme]

Next time neck down instead of up and you won't get donuts. Use .308 brass and a false shoulder.

308 brass is short