Case Head Separation

So, you wore out your brass, what's your point??
You said you got 8 firings out of them, I think that's pretty good for a high intensity rifle round where you are working the brass hard.
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When I did shoot max loads, I never went past 5 loadings. Brass wears pretty quickly with max loadings.
 
I took it as his measurements all being relative to one another on the same comparator. Typically, the radius bead-blasted onto the aluminum Hornady comparator inserts are large enough that they will read short; as little as 0.004" short and as much as 0.009" short on measurements I've made with mine.
 
Paul B. said:
If I understand you correctly, you're taking you initial measurements off a new unfired case. Try the following. It might make a difference.

This is how I set up my sizing die for bottleneck cartridges.

1. Take a once fired factory round and blacken the neck and shoulders with a Magic Marker or Sharpee pen. Some people like to smoke the neck and shoulder, but I find the Magic Marker/Sharpee pen a bit better.

2. Carefully lubricate the case.

3. Loosen the lock ring on the sizing die and back off about two turns from when the die is set to touch the shell holder.

4. Size the case. Note where the marks are on the case and turn the die down about a half a turn and size again. Turn down some more, and resize again. What you are looking for is the marks on the blackening just touching the shoulder.

5. Clean the lube from the case and try it in the rifle. It may chamber just a bit on the snug side. If so, turn the die down ever so slightly, lube and size again. Wipe off the lube and try in the rifle. If it slides in as easily as a factory round, you should be good to go. If not, usually one more very slight adjustment should fix the problem.

6. Tighten the locking ring for the die and you're done. You have just set your sizing die up for a custom fit to your specific rifle, rather than a generic one size fits all guns.

Paul B.
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I only measure the factory ammo as one reference point. In this particular circumstance, factory minimum sized cases are .002" shorter than my fire formed cases. I do not use the factory base to shoulder datum measurement as a reference to determine how to size the brass. I use the measurement I get from fire formed cases. The factory measurement was only listed in my post to show that the cases are never being worked over a great distance. The fact that I just happen to return these cases to that dimension is a coincidence.
 
Unclenick said:
I took it as his measurements all being relative to one another on the same comparator. Typically, the radius bead-blasted onto the aluminum Hornady comparator inserts are large enough that they will read short; as little as 0.004" short and as much as 0.009" short on measurements I've made with mine.
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Unclenick, this is correct, all of my measurements have been made with the same Hornady base and .420 headspace comparator bushing.
 
hounddawg said:
SAAMI specs for the datum on the 300 PRC is 2.204 - .007 @ .420. The factory would size their ammo to fit in a chamber 2.297. If your cases are only 2.191 and assuming you comparator is actually .420 that means you are sizing between .006 and .013 below what you actual chamber is.

http://bulletin.accurateshooter.com/2018/08/its-official-saami-approves-hornady-6-5-prc-and-300-prc/
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With my comparator bushing, factory Hornady ammunition measures 2.189". I have measured from several boxes and lots, they are always the same.
 
In fact, all of my cartridges read a little short when using the correct sized bushing. I don't get too hung up on a bushing not giving a reading within SAAMI spec. If I was using gauges, I might be concerned. Since I am using an imperfect comparator bushing I expect some deviation from spec. Since all measurements have been taken with the same bushing I have confidence in the validity of the measurements.
 
To add some clarification, the only reason I even bother taking measurements from factory new ammunition is so I can compare and see how far the shoulder is pushed forward from a case sized to minimum specs. I record this data with all my rifles as a part of my control set of data points. Additionally, If I find that a factory load shoots really well, I have that data to copy when trying to reproduce that factory ammunition.
 
not surprising, my Hornady .400 comparator measures my Manson gages .009 shorter than what they are marked.

Back to topic like Mehavey suggested try just neck sizing for a few firings until the bolt does not want to close on a empty case
 
hounddawg said:
Back to topic like Mehavey suggested try just neck sizing for a few firings until the bolt does not want to close on a empty case
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He already has in a way but did not recognize it .

OP said:
In the first batch of brass (before this batch) I did have some hotter loads where I had some heavy bolt lift and a stuck case. The stuck case base to shoulder measured 2.194"
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The 2.194" is likely the same measurement he will get if he neck sizes only and fires again . IMHO that is his measurement he should be bumping .002 from . So his sized cases should measure 2.192" maybe 2.191" and below the OP says 2.191 will chamber based on the cases "not sticking" .


OP said:
My chamber is snug, head space is .002" longer than the factory ammo cases were before being fired the first time. Shoulder is pushed back .002" to their original size.

Hornady factory ammunition measures 2.189". Fire formed cases both factory ammo and my loads that did not stick measured and still measure 2.191". Cases get sized so the base to shoulder measurement is returned to 2.189".
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Based on all of the above I'd say the OP is bumping his shoulders at least .005 on each firing . I believe he needs to rethink what he believes he knows and start a new using methods mentioned in this thread .
 
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But I am not actually pushing the shoulder back .005". When I said stuck case, I literally meant a vase that would not extract and had to be tapped out of the chamber with a rod and hammer. At 2.192" and some change I get heavy bolt lift and hard extraction. Cases at 2.192 and some change are difficult to close the bolt on. I still have all of the cases I gave measurements for. I can measure and test chamber fit again, bit I have already done so at least a dozen times. If I neck size only, I am nearly certain cases will stick.

I think I may try using my full length die to size the entire neck, bit I am not convinced that I am not using a solid method.
 
I'm working with 6.5 PRC cases right now--which while sharing the name, are different case lengths from the 300 PRC's--for the purposes of necking down to .257 for the .25 PRC blackjack. I'm using hornady brass because it's the only stuff I could find, and only in loaded ammo at that. I've run into an issue with repeated resizing with a few cases that were sticky in the chamber, I've found that I have to be careful about any compression of the case on the shoulder as the brass can form an outside ridge at the base of the shoulder, which in turn can cause the cartridge to hang on the chamber wall upon chambering, especially in a tight match type chamber. Not saying that's what I think you're experiencing, just putting it out there for consideration.
 
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Stag said:
...brass can form an outside ridge at the base of the shoulder,
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I'm having trouble visualizing that (since the enclosed die interior should
push any deformation into the case at that juncture.)
How does an external ridge occur ?
 
OK -- forced past first contact in bolt closing, and collapsing the shoulder in a chamber
that doesn't have circumferential support as would be found in a sizing die.
 
Measure the diameter of the base. That is supposedly a problem area of the prc. The die doesn't resize the base properly. I have some hornady 6.5 prc cases with 20 firings on them.
 
sako2 said:
Here's a discussion on the sizing problem. https://www.longrangehunting.com/threads/the-prc-die-problem.253223/page-5
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After reading this post Sako2, and re reading the advice given to me in this thread, I decided to scrap all of my measurements and sort out all my tools. I found two things that may have contributed to my issue. First, I found that I have two .420" Hornady bushings. The measurements between them are .0025-.003" difference. I was not even aware that I had more than one of these. I marked the bushing that reads shorter so I will not be using it again.

I then went back to measuring all the cases I saved. This gave me a more clear picture of what was happening now that I was using only one tool. Turns out, I was sizing the brass by about .005" shorter than my chamber's headspace. Since I was sizing the cases all the way back to 2.189", naturally they were springing back to 2.191". I use the exact same method every loading so it stands to reason that I would get the same results every time, especially since I annealed every firing. I think annealing every firing was one thing that contributed to such a consistent amount of spring back on every fired case.

As per the advice of one commentor on this thread, I adjusted my sizer die to size the neck without pushing the shoulder back. As a result the shoulders were pushed forward from 2.191" to 2.193-2.1935". I then attempted to chamber them in my rifle. To my surprise the slid right in and the bolt closed without resistance. I tried adjusting the die to get the shoulder pushed out further, but 2.1935" was the maximum measurement I was able to get. After sizing all the cases I decided to anneal the neck and shoulder in the hope that the cases would expand more into the chamber and I could get a better idea of the actual headspace for that rifle. I stayed up last night and loaded them up. Then I shot them at the range this morning.

I did see a noticeable improvement in my ES and SD number for the same load I have been shooting. When I got back to the bench I measured everything again. To my surprise, all of the cases sprung back to 2.193", which is where they were prior to firing.

Again, I backed off my die by one half turn and sized a case after annealing it. This time the shoulder was pushed forward to 2.195". This case me a considerable amount of resistance when closing the bolt. I continued adjusting the die until I got the bolt to close with just a wee bit of resistance then measured the case. The measurement I got was 2.1945" I was surprised at the amount of additional resistance that just .0005" added when closing the bolt. I am now sizing the cases to 2.193", which is .004" less shoulder bump than I had previously been using.
 
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