Case neck seperation - with pics

[Martin52]

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

Yes, a cutter closer to 20 degrees seems to be part of the solution.

 

[Martin52]

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.

I use the K&M neck turner, they are now offerring a range from 23 - 50 deg.

 

[Martin52]

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.

The main reason put forward is to prevent a donut forming.....but at the risk of too deep a cut and more problems.

 

[Straightshooter1]

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.

Hmmm??? So, you're trimming and turning your new cases before the first firing?

If so, that could actually be why you might end up cutting deeper into some cases than others as new Lapua brass can have enough variation in the head space to do that. For that very reason, I don't turn the necks until after the first firing and sometimes not until after the second firing so that the case's headspace measurement is very uniform (like I typically get +/- .0005, which a good annealing helps with). I will run my new Lapua .308 brass through my LCD and trim them before the first firing and then will anneal after every firing. I use a LCD (Lee Collet Die) most of the time to size the necks and then bump the shoulders afterwards and don't size the body. I only mention this to give you some kind of perspective that might help you solve your issue.

 

[Martin52]

Hmmm??? So, you're trimming and turning your new cases before the first firing?

If so, that could actually be why you might end up cutting deeper into some cases than others as new Lapua brass can have enough variation in the head space to do that. For that very reason, I don't turn the necks until after the first firing and sometimes not until after the second firing so that the case's headspace measurement is very uniform (like I typically get +/- .0005, which a good annealing helps with). I will run my new Lapua .308 brass through my LCD and trim them before the first firing and then will anneal after every firing. I use a LCD (Lee Collet Die) most of the time to size the necks and then bump the shoulders afterwards and don't size the body. I only mention this to give you some kind of perspective that might help you solve your issue.

Yes, a tight match chamber by preference and always fine with new brass that is turned straight out of the box - except for this problem batch of brass which I now think has suffered from a too deep cut into the shoulder. I sectioned the cases and was able to see the internal neck shoulder junction and feel the groove - earlier today I sectioned a much older large primer 0.308 case that had been put aside due to the number of reloads and guess what - there was no line.....just loose primer pockets.

 

[LHSmith]

I do not like tight match chambers -they cause the problems you are having. Brass wants to expand at firing, sizing it smaller than it has to be has you constantly fighting case expansion and overworking the brass for no gain.
Another issue is not FL sizing every time and neck sizing only at intervals in an attempt to prolong brass life - this is counter-intuitive. You are causing the back-end near the head to continue to expand each NS attempt then it becomes too large in diameter for the FL sizer to swage down properly due to spring back........remember you cannot anneal this portion of the brass.
As a rule I have always trimmed and neck-turned brass before firing- before it sees any work-hardening - again this should provide for minimal spring back.

 

[AlNyhus]

Years ago, I experienced the same thing. The solution was a cutter that matched the 308W shoulder angle.

Once the cutter angle is correct, lightly blending the cut into the shoulder works well. Using a die that sizes all the way to the bottom of the neck and pushing the shoulder back .015 or so prior to the first firing helps the shoulder/neck junction form more smoothly and helps with the whole donut issue. Pushing the shoulders back prior to firing is one of the best things you can do to prevent donuts in the first place.

Good shootin'. -Al

 

[Martin52]

Thanks for your comments. I'll try and end this post with a bit of feedback. After sectioning a few cases and taking a closer look inside, the necks appear to have separated because the original cut into the neck/shoulder junction was too deep. All fired cases showed a groove running around the inside of the neck/shoulder junction and it was deeper on those with more firings.

This is obviously due to the cutter set up but I also now think that a 'universal' cutter angle, of 50 degrees is not the best choice for a .308 case with a 20 degree shoulder, a cutter angle of 23 degrees is better.

 

[AlNyhus]

.....I also now think that a 'universal' cutter angle, of 50 degrees is not the best choice for a .308 case with a 20 degree shoulder, a cutter angle of 23 degrees is better.

No, it's not. The transition is too abrupt and you get a 'break on the line' type of situation.

My go-to neck turner is a vintage Sinclair unit with cutters hand stoned for 20, 30 and 40 degree angles as well as the supplied 50 dergee 'universal' cutter. They all work and have their place.

Pushing the shoulder back .015-.020 before neck turning and initial firing makes the exact cutter angle a bit less important.

Good shootin'. -Al