Brass Memory and Springback

[The Glockodile]

Reorganized all my old brass and came across a very special set - 100 pieces of Lapua .308 Winchester, fired 6 times - the very set that started me off with handloading so long ago.

Decided to pamper this set with a spa day.

1. Cleaned
2. Annealed with the Kiwi Device
3. Full Length Sized
4. Neck Dilated with a .307“ Carbide Expander Mandrel
5. Trimmed to 2.010,” verified neck thicknesses of 0.01450”



6. Checked necks for fit over a .306” Carbide Turning Mandrel - fit!…



7. Next morning, over the same .306" Turning Mandrel - surprise, no fit!!!

I DID account for case lip burrs as well as temperature, FWIW.

Never really thought to see this with Lapua brass.

On a similar anecdote - Ages ago, when I was still using a Tempilaq - guided Giraud… I’ve had CBC brass which was loaded the day before with neck tension that wasn‘t optimal but adequate, which ended up spilling powder all over the place as I grasped the tips to move them into some box. In this case, the “memory” sprung “the other way,” opposite to what the Lapua brass above did.

Is there any rhyme or reason to the way brass behaves, as far as this is concerned?

 

[AJC1]

Context: Reorganized all my old brass and came across a very special set - 100 cases of Lapua .308 Winchester, fired 6 times - the very set that started me off with handloading so long ago.

Decided to give this set a spa day.

1. Cleaned
2. Annealed with the Kiwi Device
3. Full Length Sized
4. Neck Dilated with a .307“ Carbide Expander Mandrel
5. Trimmed to 2.010”, verified neck thicknesses of 0.01450”

View attachment 1183233

6. Checked necks for fit over a .307” Carbide Turning Mandrel - fit!…

View attachment 1183234

7. Next morning - surprise, no fit!!! I DID account for case lip burrs as well as temperature, FWIW.

Never really thought to see this with Lapua brass.

On a similar anecdote - I’ve had CBC brass which was loaded the day before with neck tension that wasn‘t optimal but adequate, which ended up spilling powder all over the place as I grasped the tips to move them into some box. In this case, the “memory” sprung “the other way,” opposite to what the Lapua brass above did.

Is there any rhyme or reason to the way brass behaves, as far as this is concerned?

I prefer to control the inner neck dimension with mandrels vise outer. A .307 assumes a .001 springback to achieve .002 neck tension. A set of mandrels will let you dial final neck tension " hoop resistance/strength" . I over size and control expansion.... works for me. My dad used bushings and I'm pulling bullets that are in the case.

 

[NMexJim]

I've never seen what you describe with/ my .308 or any rifle brass - Lapua or otherwise.

You must be an optometrist using the word "dialated". I hate it when they dilate my eyes. Anyway, I don't think even severely hardened brass would do that. That usually results in less spring.

Did your wife change the pilot on you?? I'd check to be sure I still had the correct one in place. Check your annealing process again. Shucks man, I don't know.

 

[Bazoo]

Wow, that's wild man. I've never heard of that. Thank you for sharing your findings though.

 

[The Glockodile]

Difficult to push in the .307” mandrel after dilation, easy to get on the .306” mandrel.

That’s what’s supposed to happen…

Not supposed to pucker up the next day…

 

[N555]

If you used the AMP annealer and a minimalist sizing approach they're too soft with near non existent neck tension.
When the brass is dead softed you size with a standard FL sizer that under sizes the neck by around -.005 and then uses an expander and expand it back out to -0.002'' bullet size and that will get you very close to normal factory neck tension.
If you insist on using -.001 undersize to hold the bullet then I would recommend no annealing or using ineffective annealing such as heating to 900f or less.

 

[The Glockodile]

Edited the first post.

What explains the behavior of the brass?

 

[The Glockodile]

Know what, never mind…

False alarm.

I just didn’t push hard enough, and the necks were just “grippy” without their usual layer of carbon burnt in.

 

[GeoDudeFlorida]

Know what, never mind…

False alarm.

I just didn’t push hard enough, and the necks were just “grippy” without their usual layer of carbon burnt in.

Insert Emily Litella rant on “Grass dilation…”

 

[JFrank]

I really haven’t experienced spring back, i sized these months ago with a .261 bushing.

I don’t anneal either..

 

[film495]

Know what, never mind…

False alarm.

I just didn’t push hard enough, and the necks were just “grippy” without their usual layer of carbon burnt in.

fresh clean brass is surprisingly grippy. that burnt on layer really acts very much like powdered graphite or a dry lubricant for sure. oh, maybe that is the trick, use a bit of powdered graphite when running the test, might make it go a bit smoother .. har har

 

[Palladan44]

I had to move to a narrow base resizing die in .223 because of brass spring back down near the case head.