Neck (and body) sizing - what am I doing wrong?

[SGK]

I measured the concentricity of a fired piece of brass. At the middle of the neck it is about 1.5-2 thou max variance. I look at the same batch of cases run through my Redding Type S bushing neck sizing die (having used the body die to resize the rest) and the middle of the neck is showing 8.5 thou of variance. The wobble in the neck is very visible to the naked eye. Mid shoulder variance is about 0.6 thou. So I have knocked the necks off-centre. What am I doing wrong and how to fix?

(Forster Coax press. Titanium nitride bushings. No lube.)

 

[Bart B.]

What make?

Some military brass varies that much

 

[avidflyer]

I'd start looking at the bushing......had some bad ones in the past

 

[SGK]

PPU. But note that it is the resizing which has knocked it out of whack.

 

[Willie]

How far are you reducing the neck diameter, from fired brass to neck sized diameter? And how much of the neck are you sizing?

 

[SGK]

Bushing had some fine shavings of what I assume was brass inside it. Nothing else visibly wrong/obvious. Perhaps that was it. Do you guys chamfer and deburr before using such a die?

 

[JimSC]

Premium brass or once fired LC?

Bushing had some fine shavings of what I assume was brass inside it. Nothing else visibly wrong/obvious. Perhaps that was it. Do you guys chamfer and deburr before using such a die?

I deprime, lube, size, then trim and chamfer/deburr just before washing the cases

 

[BoydAllen]

Is the bushing loose enough to rattle when you shake the die? It should be. yes you need to square up the case mouth, chamfer and deburr, before sizing.

 

[SGK]

3x fired (but annealed)

.335" bushing. Small sample of fired brass is about 0.346".

Yes I set it so I can hear it rattle. I was unsure about trim, chamfer and deburr before versus after. I was concerned the neck sizing element would lengthen the brass as FL resizing does (albeit not to the same extent obviously).

 

[Willie]

Is the bushing loose enough to rattle when you shake the die? It should be. yes you need to square up the case mouth, chamfer and deburr, before sizing.

Like Boyd said, if you have the bushing tight, you need 1/8th of a turn for the bushing to float.

 

[SGK]

And how much of the neck are you sizing?

All the neck bar the 1mm or so at the shoulder junction

 

[SGK]

Redding instructions call for 1/16th. Maybe it tightened up. I could her it rattle though.

I have about 130+ cases that now need fixing...

 

[Willie]

You shouldn't be reducing neck diameter more than .004 at a time, use intermediate size bushings to keep from inducing all that pressure at once.

 

[SGK]

Previous to this I had used a 1 thou larger bushing (2x fired to 3x loaded). I passed the last 6 rounds with through the tighter bushing (cases had been sized with 0.336 and then 0.335) and had an improved group. Then it came to preparing the full batch again. I deprimed, cleaned, body sized and then annealed (for the first time). Then I put them through the 0.335 neck sizing die.

SPJ, nope. I had turned the high side of the brass leaving a high side of approx 0.0146" and plenty of low side, unskimmed brass. Originally I came up with a bushing of 0.308 + 2 x 0.0146 - 0.001 = 0.336 (rounded). I then tried 1 thou more neck tension. It would seem I have a SAAMI spec chamber.

I did not have this problem before today and was getting reasonably concentric loaded rounds. I think it was a case of newly annealed / soft brass, reducing too much and some shavings in the bushing (although these may simply have been from the last case rather than the cause of the problem per se).

Now I am wondering if the whole lot needs to go in the bin.

 

[SGK]

Annealing should simply make an easier job of the compression. I'm not sure why that would knock things out of alignment. Unfortunately I put the whole batch of brass through the annealer and so don't have a comparison from that batch. Anyhow... I'm wondering where to go from here. Clearly the necks need to be realigned (assuming I try to save the brass.) Run them through an expander mandrel to regain alignment then back through the body die and finally resize the necks again? Need to sleep on it.

 

[Dusty Stevens]

So you never answered the .011 sizing question? Thats about .009 too small of a bushing

 

[243winxb]

reducing too much

Yes

.335" bushing. Small sample of fired brass is about 0.346".

To much at a time.


The fix is below from Willie.

You shouldn't be reducing neck diameter more than .004 at a time, use intermediate size bushings to keep from inducing all that pressure at once.

Redding think more then .008" is to much.. Annealed may be a problem? If over done?

 

[SGK]

The only other thing I did differently was I fiddled with the large set screw on the top of the press, the one that dials down into the yoke you slide the dies into. I dialled it down more than it was before. I thought I still had the die free floating but perhaps it wasn't floating enough.

If I merely crushed the neck downwards then I'd blame (principally) too much contraction in one go and too soft brass. Everything went smoothly - I didn't even notice the issue until I had done the whole batch and was looking at them closely later when chamfering and deburring.

I do realise that with a SAAMI spec chamber turning the high side off the necks for better uniformity has led to a large release dimension (it would have been large to begin with prior to turning) and perhaps no gains to be had from the work. The RWS brass I have has an even thinner neck wall. I can't change the chamber (and on this rifle the barrels come already chambered so outside a special order to Germany, which may not even be possible, it is a dimension I have to live with).

I'm going to take another look at the screw on top of the press (backing it right out) and see if I can straighten the necks on these cases up.

Fig 6 here https://www.forsterproducts.com/pdf/instructions/co-ax_reloading_press.pdf I note "step 5" but had previously never touched this screw at all and so had thought it wasn't even enough to "keep the die lock ring under tension."

 

[243winxb]

no gains to be had from the work. (Neck turning)

My 243 win factory chamber benifits from neck turning.

But size only 1/2 of the neck. The unsided part expands to the chamber after 3 or more firing. No spring back.

No idea on press adjustment of a ForsterCoax press. RCBS here.

 

[grovey]

.346 seems on the big side . My fired lc 308 brass measures .342.5- .343 from a factory Rem chamber. Loaded rds are .336.5-.337 .