Neck turner skipping case mouth

[muleman69]

Have started turning some fired 6br Lapua brass. My turner want's to skip several thousandths at neck then will start cutting fine. Why would the neck be a tad thinner at the mouth? I have ball mic and am shooting for around .012 wall thickness which has been real consistent but It still misses a bit right at the mouth?

 

[Toolbreaker]

Previous case mouth chamfer?

 

[Nude nut]

As said above.

Cheers Trev

 

[LHSmith]

IME consistent results only come from unfired brass. Brass migrates to the neck from firing, gets work-hardened (more springy and difficult to cut) and if a bushing die was used to size-they only size a portion of the neck.

 

[243winxb]

Brass spring back after the larger expander is removed.

The turning mandrel is smaller in diameter.

Slow powders and light loading may not full expand necks to the chamber. More so with light for caliber bullets.

 

[muleman69]

Previous case mouth chamfer?

I don't think so? When I chamfer I just hit it very lightly . Most of these places are a lot wider than the chamfer

 

[243winxb]

https://thefiringline.com/forums/showpost.php?p=6589051&postcount=9

The photo and text explains it, i think.

Have started turning some fired 6br Lapua brass.

I would try fl resize in standard die. No bushing.
Expand, turn.

 

[ClassCat]

Have started turning some fired 6br Lapua brass. My turner want's to skip several thousandths at neck then will start cutting fine. Why would the neck be a tad thinner at the mouth? I have ball mic and am shooting for around .012 wall thickness which has been real consistent but It still misses a bit right at the mouth?

Your brass is flowing forward on the firing.It will be thinner at the front of the neck.Measure a piece of unfired brass for OAL,then check the fired piece for length. If that is the amount that the cutter is not cutting there is the difference.

 

[muleman69]

https://thefiringline.com/forums/showpost.php?p=6589051&postcount=9

The photo and text explains it, i think.



I would try fl resize in standard die. No bushing.
Expand, turn.

Very good info TKS

 

[muleman69]

Your brass is flowing forward on the firing.It will be thinner at the front of the neck.Measure a piece of unfired brass for OAL,then check the fired piece for length. If that is the amount that the cutter is not cutting there is the difference.

Okay THKS,I will check a bunch now then reload and shoot then remeasure

 

[ClassCat]

Okay THKS,I will check a bunch now then reload and shoot then remeasure

Don't shoot the brass first and then cut. Cut the brass out of the box and then fire form. it will grow in length , but it will do so EVENLY. Fire twice and then trim for length only.
SEMPER FI !

 

[Dusty Stevens]

Pretty typical on a skim cut. Cut more off if you gotta clean it all the way

 

[Bart B.]

All the cases I've measured have wall thickness tapering 2 to 3 times more from mouth to pressure ring. A .001" or more thicker neck at the shoulder juncture than the mouth is common. Walls are about .012" thick at their mouth to about .030" thick at their pressure ring.

The cup and draw case forming dies are made to make walls thicker near the case head so the tapered die punch can come out easy and fast of the cupping die chamber holding the case. Once the right length, its headed, shouldered, necked and trimmed to length.

 

[muleman69]

I 'm taking all this in and appreciate all the great information. Reloading now as I read this.

 

[muleman69]

Pretty typical on a skim cut. Cut more off if you gotta clean it all the way

So you are saying I should clean this up even if I'm cutting under minimum case length?

 

[Dusty Stevens]

If youre talking about turning necks and trying to uniform them yes at least 95%. If youre talking about trimming them trim to the shortest one.

 

[SteveOak]

You are seeing exactly what you think you are seeing. The thickness of the neck decreases from the shoulder to the mouth. This is a function of the drawing process, as the brass is drawn to form the case it becomes thinner.

In order for the neck to be of uniform thickness you would need to move the cutter blade in until it was removing brass beginning at the mouth. That may be thinner than you want to to be.

I just measured some cases in several places beginning at the mouth and moving toward the shoulder using one of these;





I measured 0.01180, 0.01205, 0.01220, 0.01230, 0.01235, 0.01245. 0.01265, 0.01275, 0.01285, 0.01290

This is a once fired Lapua 6BR Norma case that has been trimmed to 1.550.

 

[muleman69]

You are seeing exactly what you think you are seeing. The thickness of the neck decreases from the shoulder to the mouth. This is a function of the drawing process, as the brass is drawn to form the case it becomes thinner.

In order for the neck to be of uniform thickness you would need to move the cutter blade in until it was removing brass beginning at the mouth. That may be thinner than you want to to be.

I just measured some cases in several places beginning at the mouth and moving toward the shoulder using one of these;


View attachment 1042881


I measured 0.01180, 0.01205, 0.01220, 0.01230, 0.01235, 0.01245. 0.01265, 0.01275, 0.01285, 0.01290

This is a once fired Lapua 6BR Norma case that has been trimmed to 1.550.

So is this one case measured in ten places ? I do have a ball mic and will try doing the same. I here you on the cutter blade removing to much,I tried that and came up with around +/- .008 which to me is a bit thin.

 

[SteveOak]

Yep, one case, measured in successive places starting as close to the case mouth as I could get a measurement and progressing to as close to the shoulder as I could get a measurement.

I have seen the benchrest guys go to 0.0085". I am looking to clean up the neck so that I can spot a case that is thick on one side. This also gives me a little better control over neck tension.

 

[muleman69]

Yep, one case, measured in successive places starting as close to the case mouth as I could get a measurement and progressing to as close to the shoulder as I could get a measurement.

I have seen the benchrest guys go to 0.0085". I am looking to clean up the neck so that I can spot a case that is thick on one side. This also gives me a little better control over neck tension.

So your saying the bench guys go to .0085 neck thickness? How do you spot the thick and thin after turning?