SPRINGBACK

[Webster]

Finally got info I trust.

My question:

Does hold time in a die affect the amount of springback? In reference to sizing rifle cartridge brass? Some people think that holding the cartridge case in the die for a few seconds before removing from the die reduces springback.

RESPONSE:

Yes it does note the chart

Gazi University Scientific Research Department with 07/2013-09 project number.




Increasing the holding time restrains the shape of the bend, allowing for a period of internal stress relaxation.

A decrease in the internal stress from bending leads to decreased elastic strain, which causes an increase in permanent strain.

As the holding time increases, elastic recovery decreases.

Both the negative and positive springback angles tend toward zero as holding time increases.


I hope this answers your question.

Regards, Steve Benson

 

[Rocketvapor]

Steve,
Thanks.


I seem to be able to feel the effects of holding a few seconds when for example bumping a shoulder or collet forming a neck.

 

[Homerange]

The aspects of brass dwell time in a die is quite common knowledge here and it's more relevant when brass has work hardened. Those of us that use LCD's often use a double press with a turn of the brass between that amounts to the same as increasing die dwell time.

 

[SGK]

I wonder how many leave it in the die for a minute or more...

 

[dogdude]

I give some brass a four (sec.) count..it works..for me.

 

[Straightshooter1]

Finally got info I trust.

My question:

Does hold time in a die affect the amount of springback? In reference to sizing rifle cartridge brass? Some people think that holding the cartridge case in the die for a few seconds before removing from the die reduces springback.

RESPONSE:

Yes it does note the chart

Gazi University Scientific Research Department with 07/2013-09 project number.

View attachment 1162286


Increasing the holding time restrains the shape of the bend, allowing for a period of internal stress relaxation.

A decrease in the internal stress from bending leads to decreased elastic strain, which causes an increase in permanent strain.

As the holding time increases, elastic recovery decreases.

Both the negative and positive springback angles tend toward zero as holding time increases.


I hope this answers your question.

Regards, Steve Benson

Temperature is a factor too.

Metals are easier to form the warmer they get.

 

[natdscott]

That's the first truly original thing I have learned about shooting on the internet in a really long time.

I'll have to research the source some, and test it myself under temperature control before I am comfortable with the conclusions, but it's interesting data.

 

[Richard Coody]

Anneal for a consistent shoulder bump and consistent neck tension.

 

[searcher]

Yes, annealing makes a big difference in how "downstroke dwell time" on the press affects spring-back on the necks. Freshly annealed brass is much less subject to spring-back. Maybe .001" spring-back needing annealing and half of that annealed from what I have found.

 

[oley55]

Thank you, Steve. It is nice to see empirical evidence to confirm what we think we know. That said, the chart presented depicts times in minutes, not seconds. So one must wonder if my five count dwell time is really helping that much.

 

[Rdlningcltchdmpr]

I wonder how many leave it in the die for a minute or more...

My girlfriend says to keep it in the die for a full minute.

 

[David Christian]

Finally got info I trust.

My question:

Does hold time in a die affect the amount of springback? In reference to sizing rifle cartridge brass? Some people think that holding the cartridge case in the die for a few seconds before removing from the die reduces springback.

RESPONSE:

Yes it does note the chart

Gazi University Scientific Research Department with 07/2013-09 project number.

View attachment 1162286


Increasing the holding time restrains the shape of the bend, allowing for a period of internal stress relaxation.

A decrease in the internal stress from bending leads to decreased elastic strain, which causes an increase in permanent strain.

As the holding time increases, elastic recovery decreases.

Both the negative and positive springback angles tend toward zero as holding time increases.


I hope this answers your question.

Regards, Steve Benson

Do you have the full report? I tried to find the project number but was unsuccessful.

 

[T-shooter]

I wonder how many leave it in the die for a minute or more...

I use a K&M expander to finalize the neck tension. If any feels tighter, I just leave it setting on the mandrel for a minute or two. It does seem to help.

 

[mikecr]

I don't know. Did this somehow relate to our case resizing? How specifically?

 

[Webster]

Do you have the full report? I tried to find the project number but was unsuccessful.

I looked up the Gazi University. It's in Turkey. The author has an English name? Looks like the chart is for sharp radius bends in sheet metal. Some guys on this website say they can measure the difference between hold and no hold in the die. I don't care if there is less spring back. If you do it the same way every time you get the same result. I guess I am lucky almost every load I try shoots small. I have shot 2 ladder test and the group was under 1/2" and round in my Varmint rifle.

 

[grovey]

My girlfriend says to keep it in the die for a full minute.

She told me that too.

 

[bozo699]

She told me that too.

Bwahahaha!......

 

[Howland]

Do you have the full report? I tried to find the project number but was unsuccessful.

Your Google Fu is weak, Grasshopper.

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392017000501291

or

https://pdfslide.net/documents/the-...ers-on-springback-in-v-the-evaluation-of.html

The study was done on sheet metal, not catridge brass but I would expect it's conclusions to bear some relationship to brass.

 

[avidflyer]

been thinking about this the last couple years...if u clean and prep 400 pieces of brass in the winter how is it in the spring? Need to grab 8 pieces and do a controlled test all same lot half annealed half not then half fls and then fls and expanded with mandrel. pin gauge inside mic outside every week

 

[sqrlgtr]

Bwahahaha!......

told me same thing also...couldnt resist