Round #2. I grabbed 10* more 7mm Rem Mag cases and took measurements pre-sizing, post-sizing, and loaded with Hornady 154g SP.
Pre Neck Thk Pst Neck Thk Pre Neck RO Pst Neck RO Post Case Len Loaded RO
1. 0.0015" 0.0015" <0.001" <0.001" 2.494" <0.002"
2. 0.0025" 0.0025" <0.002" <0.002" 2.493" 0.0075"
3. 0.001" <0.001" 0.001" 0.0015" 2.493" 0.003"
4. 0.0015" 0.000" 0.0015" <0.002" Hornady Frontier brass, not used
5. 0.002" 0.002" 0.0025" 0.001" 2.492" <0.002"
6. 0.001" 0.0015" 0.001" 0.0015" 2.493" 0.002"
7. 0.004" 0.0045" 0.002" 0.0025" 2.489" 0.007"
8. 0.003" 0.003" 0.001" 0.003" 2.490" 0.0085"
9. 0.001" <0.001" <0.001" <0.002" 2.500" (2.489") 0.004"
10. 0.002" 0.002" 0.001" 0.0015" 2.491" 0.003"
11. 0.0015" 0.002" 0.001" <0.002" 2.492" 0.003"
* Case #4 was Hornady Frontier brass mixed in with Winchester. It wasn't measured for length or loaded.
Neck thickness variation mostly stayed the same between pre-sizing and post-sizing. Again, in some cases it decreased (#3, #4, #9) in others it increased (#6, #7, #11).
It appears as if every case that had pre-sized necks with a thickness variation <= 0.002" made reasonably straight ammo. Anything above that made
very crooked ammo.
The biggest surprises were #2 and #9. #2 had only 0.0025" neck thickness variation and less than 0.002" neck run-out. However, when fully assembled it had a whopping 0.0075" loaded run-out. #9 had excellent neck thickness consistency and reasonably low post-sizing neck run-out, however it's loaded run-out was 0.004". Not bad, but higher than I expected.
I loaded all 10 rounds with the same primers, powder charge, and bullets and separated the best 5 rounds and the worst 5 rounds into two groups. I will use the Tru-Angle tool to correct the worst 5 rounds so all have a loaded run-out of 0.003" or better. Then I'll shoot both groups at 100 yards (the furthest any close range around here goes) and see if there is any measurable difference between corrected rounds and non-corrected rounds.
It's nice being able to measure neck thickness variation and case neck run-out. It shows another piece of the puzzle in loaded ammo run-out.