Neck Tension vs Arbor Press Reading

mbeavers1

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Minuteman
Nov 27, 2019
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Montgomery, TX
I am just starting on my second firing of my 6br brass and things seem different on the neck tension side than the first firing.

For the first firing, I mandreled with a 0.2435" mandrel then chamfered/deburred. After spring back, I measured the neck OD at 0.268". I then seated with a K&M arbor press w the force pack and got a reading of ~0.005". Seated OD of my necks was 0.269", so 0.001" of neck tension. The gun shot great for all 800 rds.

For the second firing, I tumbled in rice, annealed using a Aztec code on Amp, sized w a Harrell's die using a 0.266" bushing, mandreled with a 0.243" (0.2435 seemed a bit to much this time), trimmed/chamfered, and started to seat. I am reading like 0.012-0.015" on my force gauge now (like 3x), but I still have about 0.001" of neck tension.

Any idea what could be going on? I mean, the neck OD still says I have 0.001" of tension but why would it take so much more pressure to seat. It physically feels like more with the Arbor press.
 
It's the AMP...


 
What you see on the seating force gauge is not purely a function of the neck sizing / expansion process. It's a large part, but not the whole story. The condition of the neck ID makes a big difference in what you 'see' or 'feel' when seating the bullets.

Here's some recent info from a pretty good shooter (Lou Murdica). He used one of the new (prototype) AMP bullet seaters, but I think you can see/feel similar results with a regular arbor press like what you have.
 
It's the AMP...


Interestingly, your first link was me..again!

I changed up my process after that. Once I size (after annealing), I tumble again in rice for 20-30min. Then lube necks w OneShot on a qtip, mandrel, trim, then charge seat.

So seems the oxide layer is still causing problems. Hmmm....