questing re: using powered neck turning lathe

[hkfan45]

Hi,

I am using the Becigneul Case Turning Motor. See The Rifleman's Journal: Good Stuff: Becigneul Case Turning Motor

I seem to be experiencing additional runout after I neck turn. My procedure is as follows:

1. Take once fired lapua brass from my rifle, FL size down (no expander ball)
2. Use sinclair expander mandrel
3. Check runout at neck (usually 0.0015)
4. Lube inside of neck and turn using the powered lathe and the 21st century case holder attached to the lathe.
5. Check runout is now 0.0025 - 0.003.

So, it seems that neck turning adds at least 0.001 of runout. Why is this? Am I doing something wrong? Is there a certain technique I'm missing when guiding the neck turning arbor onto the case?

Thanks.

 

[hkfan45]

any ideas? The arbor on the case neck is extremely tight, even with plenty of lube (imperial). Could this be it? Any other ideas?

 

[427Cobra]

After fire forming there shouldn't be any run out, I wouldn't swet it

 

[AZ.noob]

Neck turning puts a bunch of torsional load on the cases, I have the same thing happen with a cheapie Lyman hand-crank deal. One more pass through the full-length resizing die straightens them right back up again. Yes, it works the brass... another good reason to anneal regularly.

I've found that freshly annealed case necks are far easier to cut, either for length or neck wall thickness. Makes sense... it takes less effort to abrade an annealed (soft) metal than it is to do the same to a tempered/work-hardened metal. Bullets glide in very smoothly during the seating process too. Annealing 'standardizes' all your case necks (in metallurgical terms), while dramatically extending their service life. Win-win-win.

I don't mean to hijack this thread, but there's a lot to be gained by annealing. It's a simple process, and doesn't have to cost much at all.

 

[MajorHeadTrauma]

What the two previous posters stated. You will be cool the after you fire them and resize.

Also as stated, ANNEAL.


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[ZiaHunter]

Try neck turning during initial case prep on new brass. I have turned once fired brass and the neck was always tight on the mandrel after running it through the expander.