Brass spring back

[The Oregonian]

How quickly does brass spring back? Reason I ask is I am curious how it may impact neck tension. Say you sized a neck 5 mins ago, and pulled out pieces of brass that you sized 5 days, 5 weeks, and 5 months ago. Would they all have the same neck tension (not talking about to the 10th decimal, just maybe half a thou or a thou).

 

[MagnumManiac]

Try this; run a piece in your sizing die in and out in one motion, measure, do the same on another piece but hover at the top for 3 seconds, repeat with another piece, hover for 5 seconds and so on measuring each time.
You will see a point where the brass springs back less.
Also, as brass work hardens, spring back is reduced, which is why seating pressure increases on brass with many sizings and no annealing.

Cheers.

 

[GLTaylor]

MagnumManiac offers good advice. Overall, however, annealing is the best way to achieve uniform neck tension, and consistent springback - whatever it is. My experience has been (I think) brass springs back to it's relaxed state in just a moment, and then stays put wherever it is. I have had brass that was prepped for loading for upwards of 2 years that did not change.

 

[Mikecr]

Not a metallurgist, but I believe the concern is described as 'CREEP'.
When artificial stress(our sizing) is removed the brass recovers it's strain, releasing most energy added, -but not all of it,, and not all at once.
It may be prevented from doing so by it's grain structure. However, over time, there can be grain boundary sliding which can allow further deformation (from what seemed stable at first).
This is more likely to occur in work hardened brass, as there are more grain boundaries present.

There are 3 places I've run into it in reloading: Neck sizing, shoulder bumps, and primer seating.
What I've seen is continued countering of last sizing action, over time.
My last action with necks is normally expansion, and a month later neck ODs reduce further(~1/4thou).
If my last neck action was downsizing, then I could expect neck ODs to grow a bit over time.
My shoulder bumping is 1thou for immediate ammo use, but I've learned to go 1.5thou for stored ammo.
Similar with primer seating, I seat to 2thou crush, but this reduces over time. So for stored ammo, I go 4thou crush.

I'm sure I could anneal necks & shoulders more often to mitigate this.
Nothing I can do about primer cups/pockets other than compensate.
As far as neck tension, I do not believe creep affects it -while necks are at 1thou or more interference to bullet seating.
If your last neck action was downsizing to leave only 1/2thou interference to bullet(after spring back), then I would worry about tension, or at least pull friction, dropping too low for stored ammo. In a couple months you could probably pull those bullets by hand.

 

[The Oregonian]

Thanks...I go down .003 from a seated round with a bushing die and then expand with a .02 under mandrel.

 

[dok7mm]

For the most consistent neck tension I've been able to achieve, I start with sorted brass, then turn necks to .004" +/- chamber neck clearance. I believe this to be significant in the long run.

After each firing, I anneal, resize, trim and chamfer. For awhile I used Redding FL bushing dies sizing necks about .004", then using either .002" or .0015" mandrel under caliber. I have since moved to mostly Forester FL dies with expander ball removed, then using the mandrel.

I process my brass and store it until I get ready to load. I then apply Imperial dry lube to FL sized brass necks with a Q-tip and run my expander immediately prior to charging and seating the bullet. Also, I'm weighing powder charges to .02gr.

For me, this has worked for single digit extreme spread across 5 & 10 shot groups IF my load workup is correct.

Setting neck tension with a mandrel just prior to reloading seems to be beneficial, but some cases will not shoot with the rest regardless, so they go to my fouler box. I suspect case capacity is the cause.

 

[bill123]

Also, as brass work hardens, spring back is reduced, which is why seating pressure increases on brass with many sizings and no annealing.

Cheers.

I thought that in an annealed state, necks will not spring back much at all, and that's what gives uniform neck tension w/ annealed brass. As you fire and resize w/o annealing, neck become harder and spring back more until the point where they are work hardened enough to be brittle and eventually split.

 

[Orange Dust]

I will say this: If you fully match prep your brass including turning the necks to a consistent thickness, anneal the brass, and shoot HBN coated bullets, you can achieve velocities so consistent in a big magnum that you will think your chrono is broke with proper load development. The smaller the capacity of the cartridge, the more you can fudge and still get acceptable results.

 

[MagnumManiac]

I thought that in an annealed state, necks will not spring back much at all, and that's what gives uniform neck tension w/ annealed brass. As you fire and resize w/o annealing, neck become harder and spring back more until the point where they are work hardened enough to be brittle and eventually split.

No, the opposite is true to what you say, when brass is hardened, it fractures because there is no flex, which is what spring back is.

Cheers.