Case neck seperation - with pics

[Martin52]

Interested in your thoughts on this 'new to me' problem.

Case necks broke off on firing, lodged in chamber, extracted OK with no damage.

Lapua palma brass, neck turned to 0.0140, annealed, FLS, fired 8 times.

Moderate 45 gr H4895 load, Berger 155's.

Bore scope pic shows a groove inside the case neck at the neck/shoulder junction. This runs the full inside circumference and can be felt with a bent pin. It runs horizontal, or parallel to the case mouth, not vertical. It is a groove, not a raised band.

I think it is most likely due to the neck turner cutting too deep into the shoulder. I have checked all my other cases, all have this line and it is more obvious with the cases that have been fired the most.

I'd be interested in your thoughts.

 

[jackieschmidt]

What I your neck turning procedure?

I assume the necks were turned before any firing.

I have seen necks do this when shooters attempt to neck turn fired cases while using just a bushing die that does not size the neck all the way to the shoulder.

 

[Martin52]

I trim new cases before firing then use a K&M expander and turner.

After the first firing, I anneal then FLS using a custom bushing die, but with no bushing, so effectively a body die. I then size the necks with a Lee Collet die.

 

[Uthink Uknow]

Have you been bumping the shoulder back too much in an attempt to size the base a little smaller? That will produce case neck separation.

 

[Martin52]

I have had a problem sizing the base of these cases but have not let this affect the shoulder bump.

I bump the shoulders 0.0015 after each firing. The base of the case by then has expanded to ~0.4695/.4700 and is bordering on a tight fit in the chamber, but manageable. I don't think the die is the cause of the case neck separation, I think it's a cutter issue. I believe the standard K&M cutter is 50 deg. and I may need something closer to the 20 degree shoulder angle of a .308 case.

 

[KY_Windage]

I think it is most likely due to the neck turner cutting too deep into the shoulder.

So do I. I suspect you are weakening the metal and then subsequent FLSizing is making it collapse and form the groove.

IMO you should not be cutting into the shoulder AT ALL.

 

[Martin52]

So do I. I suspect you are weakening the metal and then subsequent FLSizing is making it collapse and form the groove.

IMO you should not be cutting into the shoulder AT ALL.

While I've been looking into this problem I have compared the depth of my shoulder cut with various articles that generally suggest (and some recommend) a cut into the shoulder of up to 1/32 inch. They may however be wrong. I'm within 1/32 and I think that's the problem - a less than ideal cutter angle could also be contributing.

 

[LHSmith]

So it's a tight neck .308 Win.?

 

[Martin52]

Yes, it's 0.340.

 

[LHSmith]

I have had a problem sizing the base of these cases but have not let this affect the shoulder bump.

I suggest you fix this first. Was the "custom" die made for your chamber and by whom?

 

[Martin52]

I suggest you fix this first. Was the "custom" die made for your chamber and by whom?

I do need a new custom die, I just haven't figured out who to go to. The current die made by a well known reputable company who have told me the gap is ok. It was made using fired cases not a reamer print. Previously I used a standard Forster FLS die with just the neck honed but last I heard Forster had suspended all custom work.

 

[KY_Windage]

While I've been looking into this problem I have compared the depth of my shoulder cut with various articles that generally suggest (and some recommend) a cut into the shoulder of up to 1/32 inch.

To me that is just dumb. The only (good) reason to neck-turn is to achieve consistent neck-tension, and you are not going to be any more consistent by cutting into the shoulder, and it is dangerous. Due to small variations in case dimensions it is very easy to move a case just a little too far into the cutter.

 

[TIMO]

I have had a problem sizing the base of these cases but have not let this affect the shoulder bump.

I bump the shoulders 0.0015 after each firing. The base of the case by then has expanded to ~0.4695/.4700 and is bordering on a tight fit in the chamber, but manageable. I don't think the die is the cause of the case neck separation, I think it's a cutter issue. I believe the standard K&M cutter is 50 deg. and I may need something closer to the 20 degree shoulder angle of a .308 case.

Contact K&M, they have a cutter that is angled for the 308 Win. It will make all the difference.
spare-cutter-selector
Tim

 

[243winxb]

After the first firing, I anneal

necks

Would a good annealing before firing make a difference? Jackie Schmidt link with photos. But necking up 6BR to 30 is different.

Factory annealing issue?

How much stretch when fire forming to chamber? Head to datum, factory vs fired.

If not a neck turning issue?

Watching to learn.

 

[Straightshooter1]

I have had a problem sizing the base of these cases but have not let this affect the shoulder bump.

I bump the shoulders 0.0015 after each firing. The base of the case by then has expanded to ~0.4695/.4700 and is bordering on a tight fit in the chamber, but manageable. I don't think the die is the cause of the case neck separation, I think it's a cutter issue. I believe the standard K&M cutter is 50 deg. and I may need something closer to the 20 degree shoulder angle of a .308 case.

I believe your are right about this being a "cutter issue" where you're cutting too deep into the shoulder and maybe also doing so with cutter that's at the wrong angle. And looking as your pictures, that's what it looks like to me.

A shooter next to me at the range not too long ago was having neck separation with his .243 and didn't know why. As we were talking I asked if he turned his necks. He affirmed that he did and looking as a couple of his fired case it looked to me like it very much had to do with the neck turning he was doing.

So, I highly suspect that's what happening with you.

I also turn all my .308 cases, but with a Sinclair neck turning tool and I just touch the shoulders enough to see a very small amount of material removed there. I've done this and reloaded thousands of times with a number of different case manufacturers (Lapua, Peterson, Federal, PPU, and more) and not had any issue with neck separation. You can see in the picture below what my neck/shoulder junctions looks like after turning in the picture below:

 

[FNSafari]

Good comment about making sure the angle of the cutter is in synch with the case shoulder angle. I think its PMA tool that sells cutters for the Pumpkin. Note they have several shoulder angles available and a blurb about matching you case with a cutter.

 

[338 dude]

While I've been looking into this problem I have compared the depth of my shoulder cut with various articles that generally suggest (and some recommend) a cut into the shoulder of up to 1/32 inch. They may however be wrong. I'm within 1/32 and I think that's the problem - a less than ideal cutter angle could also be contributing.

If the cutter angle and does not match the angle of the shoulder yes you would be cutting deeper into the case itself which is definitely not a good thing

 

[Curmudgeon]

I have not seen a 50 degree cutting tool. I cut 40 for an Ackley and Dasher and 35 for ‘06 and 6.5x47. 50 is considerable. Check with PMA for correct tool. Just my thoughts.

 

[Martin52]

Would a good annealing before firing make a difference? Jackie Schmidt link with photos. But necking up 6BR to 30 is different.

Factory annealing issue?

How much stretch when fire forming to chamber? Head to datum, factory vs fired.

If not a neck turning issue?

Watching to learn.

That's an interesting thread. Could be a factory annealing issue although because the fault line is quite pronounced inside the neck at the junction with the shoulder I am thinking its due to a) cutting too deep and b) wrong cutter angle selection.

 

[Martin52]

I believe your are right about this being a "cutter issue" where you're cutting too deep into the shoulder and maybe also doing so with cutter that's at the wrong angle.

Good looking brass. My cases do show a slightly deeper cut into the shoulder. I'll have to adjust the depth and also speak with K&M about the cutter angle.