6PPC brass neck spring back

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russell m

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How many times can a case be fired before the spring back starts going away? Which with my logic changes neck tension. russell m
 
I shot mine for the whole season last year and had no problems with neck tension.
 
russell m said:
How many times can a case be fired before the spring back starts going away? Which with my logic changes neck tension. russell m
Click to expand...

Hear me out here Russell :)

Picture to hunks of metal formed into a "spring." One is made of hard spring steel and the other is made of lead.

Which one springs back better?

Old workhardened brass is "spring steel."

New or annealed brass is "lead."

I will often fire a case 50 times without annealing, IME springback INCREASES with hardness....

al
 
Maybe Artintx will pipe in. He had a few links on another thread.
Seems that after letting rounds sit a while. It is harder to pull bullets. This has been my experience. And this will very.
 
Same thing happens when you neck expand prior to turning. Some advocate expanding and then immediately turn the neck. When I don't turn the case right away after expanding, the brass will not easily go over the turning mandrel, ie. the neck diameter shrunk. I imagine that loaded cases sitting for a while might do the same, or try to, considering there is a bullet in the way.
 
alinwa said:
... springback INCREASES with hardness....

al
Click to expand...

Right. The yield stress increases as the material work hardens, while its elasticity remains constant, which means that the strain to yield increases. That's why you may, as the brass is fired and resized over and over, need to go to a smaller bushing to get the neck to hold a bullet. The work hardened neck springs out to a larger diameter after sizing than the annealed neck.

Cheers,
Keith
 
Remember, if you oversize then expand up, the springback is towards being tight, having greater tension. -- spring back is always toward the last dimention. I have been known, with hard brass, to size just a bit more than needed, then do a final pass with an expander mandrel. (Not in a sizing die, but a polished mandrel like you'd use for expanding prior to neck turning.) Some cases barely move, some might be opened up an extra .001 or so. This for long-range stuff. More work, but neck tension is incredibly even.
 
mks said:
Right. The yield stress increases as the material work hardens, while its elasticity remains constant, which means that the strain to yield increases. That's why you may, as the brass is fired and resized over and over, need to go to a smaller bushing to get the neck to hold a bullet. The work hardened neck springs out to a larger diameter after sizing than the annealed neck.

Cheers,
Keith
Click to expand...

That, and necks get thinner with age ;)

Brass which reacts less to sizing also reacts less from the firing event.

I've got brass that's been fired so many times that casenecks which used to "hold a bullet" after firing and that I sized with .XXX bushing now will no longer hold a bullet, AND needs a smaller bushing. :)

It's harder, springier and thinner.

al
 
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