Case Head Separation

[kilotanker22]

Here's a discussion on the sizing problem. https://www.longrangehunting.com/threads/the-prc-die-problem.253223/page-5

Now, as for the problem discussed in the above link. I decided to measure the cases at and just in front of the web. Virgin Hornady cases measure .527". Fired cases measure .531", and my sized cases measure .530". Head diameter on the Hornady cases measure .527". Neither my fire formed or sized cases give me any trouble chambering. I will keep an eye on this. To be honest, I did not even realized that could be an issue on a non-belted case.

 

[kilotanker22]

Do me a favor:

Unscrew the sizing die a turn+1/2 (way clear of the shoulder)
Start sizing a fire case, chambering it, and then size again +1/8th turn (or less).
Repeat.

Sooner or later the case will have squeezed to a longer length to where the bolt starts having trouble closing.
What's the comparator measure as case headspace dimension at that point?



postscript: Use that point as reference to push the shoulder back 2-thou, not the as-fired size.

.

This was excellent advice... I sure thought I had it figured out. I am a proud man and stand by my work, but I am also an honest man. I was mistaken. Your post helped me to find part of my error.

 

[Metal god]

Turns out, I was sizing the brass by about .005" shorter than my chamber's headspace.

Based on all of the above I'd say the OP is bumping his shoulders at least .005 on each firing

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"

Glad Sako could help .

 

[kilotanker22]

Glad Sako could help .

You were damn close with your prediction. I appreciate the help.

 

[tangolima]

0.005" head clearance is close to being excessive. You are actually doing not bad getting 8 firings with such high pressure round. I wouldn't be surprised to get over 15 firings if you reduce the head clearance down to 0.002”. Glad that you figured that out. As you can see, it isn't hard even without fancy tools.

Your latest measurement results are also interesting. 2.1945” you could close the action with little or no resistance. 2.1950” the resistance became very noticeable. That's half a thou more. I really doubt you can close the action at 2.1985", or 4 thou more.

You sized the brass to 2.1945" and fired them. After firing, they became 2.1930", or 1.5 thou shorter. That's probably how much the firing pin impact had shortened the brass.

-TL

Sent from my SM-N960U using Tapatalk

 

[hounddawg]

grats on getting it figured out

 

[kilotanker22]

0.005" head clearance is close to being excessive. You are actually doing not bad getting 8 firings with such high pressure round. I wouldn't be surprised to get over 15 firings if you reduce the head clearance down to 0.002”. Glad that you figured that out. As you can see, it isn't hard even without fancy tools.

Your latest measurement results are also interesting. 2.1945” you could close the action with little or no resistance. 2.1950” the resistance became very noticeable. That's half a thou more. I really doubt you can close the action at 2.1985", or 4 thou more.

You sized the brass to 2.1945" and fired them. After firing, they became 2.1930", or 1.5 thou shorter. That's probably how much the firing pin impact had shortened the brass.

-TL

Sent from my SM-N960U using Tapatalk

I sized them 2.193", and when they were measured after being fired and decapped, they still measured 2.193.

 

[Metal god]

I sized them 2.193", and when they were measured after being fired and decapped, they still measured 2.193.

That should be perfect , your brass should last at least double the number of firing now maybe triple .

 

[tangolima]

I sized them 2.193", and when they were measured after being fired and decapped, they still measured 2.193.

Ok, I thought you stopped at 2.1945", which I believe is your rifle's headspace. Quite likely that the chamber pressure stretched the brass from 2.1930" to 2.1945", and it sprung back to 2.1930" when the pressure subsided. In other words, the firing pin impact didn't change anything significantly.

If it is for range shooting, I probably would size it to 2.194" for longer brass life. For hunting, I would size it to 2.1925" for more reliability.

-TL

Sent from my SM-N960U using Tapatalk

 

[RC20]

This thread is interesting . The OP is certain he is sizing his cases Correctly . Why are so many trying to fix things that ain’t broke ? FWIW there might be a bit of sarcasm here haha

Well, he brought it up! And yes the following is just my opinion for whatever it is or is not worth. Its good to have discussions that may help others or even the OP.

And I agree with the test it, not measure it. Ergo, can you slip a fired case back into the chamber? That is the real test, any other device has some degree or error and we are not talking much.

It certainly sounds like excessive set back of the shoulder.

When I measure a fired case and size it with a set back, I test the case in the gun again. I do a minimum and expect some cases not to let the bolt close right (note, old Sako's have a very tight bolt so you need to do it on an empty chamber to know how much resistance to closing there is)

I have done thousands of cases and since I did the minimum set back, I wear out the primer pockets before a case head crack. 8 firings with being careful on set back should get you at least 20 firings.

 

[kilotanker22]

Well, he brought it up! And yes the following is just my opinion for whatever it is or is not worth. Its good to have discussions that may help others or even the OP.

And I agree with the test it, not measure it. Ergo, can you slip a fired case back into the chamber? That is the real test, any other device has some degree or error and we are not talking much.

It certainly sounds like excessive set back of the shoulder.

When I measure a fired case and size it with a set back, I test the case in the gun again. I do a minimum and expect some cases not to let the bolt close right (note, old Sako's have a very tight bolt so you need to do it on an empty chamber to know how much resistance to closing there is)

I have done thousands of cases and since I did the minimum set back, I wear out the primer pockets before a case head crack. 8 firings with being careful on set back should get you at least 20 firings.

I think you are right on. As I noted in one of my recent posts, I was wrong.