Brass springback over time

[FTR_Mojo]

Hello all,

My once fired, annealing .308 lapua brass was all full length resized down 0.002 to 1.479 BTO. I measured almost every piece and they had no runout.

They were then cleaned in a tumbler with warm water.

That was 1 week ago. I have come back to reload them and they mostly now measure 1.480, with a fair few at 1.481.

I was under the impression that springback happens very quickly after sizing. But I'm seeing a relaxing of the brass to the tune of up to 0.002 after a week.

Would the warm water have caused this springback? Or is it just a function of time? Or is this just a common phenomenon for newer brass? It is rather frustrating, as whilst most pieces have relaxed to 1.480, there are some that didnt and some that went all the way back to 1.481. It would interesting to understand what happened....

I'm travelling to compete abroad for the first time next year, so need to load up a lot of rounds ahead of time. Id rather go with rounds that have the same headspace.

Thanks!

 

[Fairchaser]

Brass is an ever changing thing. I think spring back can take some time as well. I wait 24 hours after annealing with an AMP machine to size my brass and then size twice and use a 2-5 second dwell time. In the end, you can sort out the anomalies if you want. I don’t wash or tumble my brass anymore. I would start there to see if that helps.

 

[FTR_Mojo]

Due to the volume of brass I think I did end up waiting 24 hours before sizing. And do the same as you when sizing.
Maybe I should just size a thou smaller in future... 1.478
And use cold water to tumble wash...
Like you say, could just be one of those things. Another thing to measure

 

[60723]

I assume you mean base to shoulder. I anneal every firing and size down about .002. I leave cases in die about 6 seconds. Measured some that have been loaded 3-4 weeks and get the exact measurement as when first sized. I don’t see my brass growing after sized. I also don’t clean my brass. Don’t know if the hot water does anything.
I would strip the bolt and make sure everything chambers ok after you clean the brass. If so, go shoot. If not, go down .001
Make sure to keep your comparitor of choice clean! Good luck.

 

[L.Sherm]

Try not washing and non annealed it may surprise you.

 

[rwj]

Do you perform any neck sizing operations (bushing or mandrel) after cleaning? If yes, you may want to compare the before/after base to shoulder dimensions to determine if the operation is the culprit.

 

[64Rambler]

Yep, I've seen the same thing with different neck bushings. For my 6BRA, if I use a 266 or 267 bushing, the necks come out at that number and they stay there. If I go down to a 265 bushing, I initially get 0.263". If I let it sit a week or so, I get a mix of everything from 0.263" all the up to the desired 0.265". Can you say variable neck tension? Perhaps I'm not annealing enough?

 

[L.Sherm]

Perhaps I'm not annealing enough?

Perhaps annealing is the problem.
I've found spring back is alot more controllable by not annealing. Wether its .0005 or .001 as long as its consistent.

 

[rwj]

Perhaps annealing is the problem.
I've found spring back is alot more controllable by not annealing. Wether its .0005 or .001 as long as its consistent.

Interesting, my experience is exactly the opposite. When I started annealing with an AMP machine after each firing, my sizing results became very consistent. But it would seem reasonable to expect the same sizing outcome by consistently not annealing.

 

[DumpHollow]

Are you flame annealing or using an AMP?

 

[64Rambler]

Are you flame annealing or using an AMP?

Flame. Would love an AMP, but ouch!

 

[FTR_Mojo]

Do you perform any neck sizing operations (bushing or mandrel) after cleaning? If yes, you may want to compare the before/after base to shoulder dimensions to determine if the operation is the culprit.

I expand using a mandrel as a last step. Id be surprised if that was causing the shoulder to move. But worth a test.

 

[Coyotefurharvester]

I have seen this with range brass(223) when I prep 100-500 cases and they sit for several months before loading. I avoid any issues by plunk testing each case in an ammo checker before loading. Usually see a handful out of 100 that don't drop in clean. Depending on head stamp, sometimes I just scrap them. I don't see the spring back with storage of single rifle use brass. But I usually don't have brass sitting long before loading. I just sized some 30/06 brass(not annealed), won't be loaded at least until spring. I'll check it again with checker see if there is a change.

 

[FTR_Mojo]

I assume you mean base to shoulder. I anneal every firing and size down about .002. I leave cases in die about 6 seconds. Measured some that have been loaded 3-4 weeks and get the exact measurement as when first sized. I don’t see my brass growing after sized. I also don’t clean my brass. Don’t know if the hot water does anything.
I would strip the bolt and make sure everything chambers ok after you clean the brass. If so, go shoot. If not, go down .001
Make sure to keep your comparitor of choice clean! Good luck.

Sorry, I did mean shoulder.
I'll try dwelling even longer. Cant hurt.
And I think I'll use cold water too.

 

[JFrank]

@FTR_Mojo
Will the brass that you’ve discovered longer after sitting, still chamber freely and how close to a fired case dimension are these cases that have grown in length ?

 

[FTR_Mojo]

@FTR_Mojo
Will the brass that you’ve discovered longer after sitting, still chamber freely and how close to a fired case dimension are these cases that have grown in length ?

Yes, they will chamber. And freely. Even the ones that have sprung back to fired dimension.
There were a couple (out of 250) that had bizarrely sprung back to 0.001 over my fired dimension. I could chamber them, but there was a touch of resistance. So I will resize those again.

 

[JFrank]

A follow up question; Have you measured the case neck OD after sizing and after the same time period ?

 

[FTR_Mojo]

A follow up question; Have you measured the case neck OD after sizing and after the same time period ?

No I havent.
I expand my necks as a final process, right before I seat. So it didnt occur to me to do that.

 

[JFrank]

I don’t anneal and from a long range Benchrest shooters perspective, take this as you will.

I never see neck OD spring back even after a couple months, I burnish the layer of left over carbon with a bore brush just prior to seating to get remarkable seating consistency.
My observations:
Bullet hold variation changes targets, seating depth from shoulder to bullet ogive changes targets but a thousandths of headspace doesn’t seem to make any difference unless the case won’t chamber freely or extract leading forcing a bolt open.

 

[FTR_Mojo]

Thanks JFrank.
It could be im worrying about nothing. As you say, they chamber just fine. And the rifle does shoot great.

I was just surprised and disappointed by the change in shoulder. Given how much time and effort I put into brass prep.

I'll make a few small changes to my process and see if I can stop them spring back.