Neck sizing in steps, does it reduce hardening?

[TimK]

I've received some advice that says neck sizing my brass down from 0.344" to 0.336" is best accomplished in two steps, say a 0.340" bushing then a 0.336" bushing. The claim is that going in steps reduces the associated work hardening. It's an issue for me because I'm getting neck splits in some Lapua brass after just a few loadings.

I've got a little metallurgy in my background, and I can't come up with a good reason why going in steps should make a difference unless there is some annealing between them.

What do you think?

 

[pacificnw]

Re: Neck sizing in steps, does it reduce hardening?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">When you squeeze the neck down more than a 'certain' amount, you lose what we call 'spring back'. This is the ability of soft brass to actually move back out a small amount, usually .001". So if you select a .336" bushing, you will size that down to a point and the brass will spring back yielding an O.D. of .336".

Unfortunately, if you attempt to size back down more than say .005" at a time (Redding throws out .007"-.008"), you will not get that spring back, so your .336" target point might be only .335", which isn't the end of the world, but most of us here will step down if we have to go more than than .005" amount.

The way we get around this is by using a intermediate 'step down' bushing, to do the total sizing in two, or even three moves. Take a fired case from your rifle, measure at the case mouth and see what you get. My Savage rifle blows out my necks to .343"-.344", so I use a .339" or a .340" (<.005" step) and then I'll use my final bushing.</div></div>

ChrisGarrett wrote that in a response to me yesterday in another thread

 

[Fuzzball]

Re: Neck sizing in steps, does it reduce hardening?

"I can't come up with a good reason why going in steps should make a difference.."

You are correct, what work hardens brass and changes its "spring back" is what's done to it, there's no magic in how many steps it takes or how it's done.

The real reason for necking down in smaller steps is that it tends to make straighter necks. No seater can seat concentric bullets in tilted necks.

I prefer Lee's collet neck sizers rather than bushing sizers when working with factory chambers. The resulting necks on each case will be as straight as possible.