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Factory Ammo Pierced Primer

 
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  #15  
Old 08-23-2007, 04:58 PM
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Catshooter

I've looked at a few primers in my time but readily admit, I dont know what I'm looking at and so do not how to read them. Your advice is a great help to us so many thanks for not letting the sun go down on a day when I haven't learnt something.

I know Brown Dog will appreciate all your time taken to help and your clear easy to understand advice.

.

.
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  #16  
Old 08-24-2007, 05:28 AM
ds ds is offline
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Cat Shooter,

Is it possible to get the same result with very soft primers, rather than the load being over pressure. the reason being.....

. S&B load is very sedate. 40.5 grains of S060/2.....which is the same powder as AA2015 behind a 167 grain Sierra MK.

. S&B primers are known to be soft.....when CZ tested a couple of hundred CZ 700 rifles they had "light stikes" with Norma Diamond line and no problems with S&B. I have tried CCI BR primers and found the same thing as the Norma Diamond line in my CZ700 - S&B work without a problem, hence my belief S&B primers are much softer.

. Also Brown Dogs rifle is a AI AW......chamber is set to max headspace.....if it makes a difference.

Only thoughts,

David.
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  #17  
Old 08-24-2007, 08:19 AM
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Quote:
Originally Posted by david shone View Post
Cat Shooter,

Is it possible to get the same result with very soft primers, rather than the load being over pressure. the reason being.....
Yes!

Quote:
"... S&B load is very sedate. 40.5 grains of S060/2.....which is the same powder as AA2015 behind a 167 grain Sierra MK.

. S&B primers are known to be soft.....when CZ tested a couple of hundred CZ 700 rifles they had "light stikes" with Norma Diamond line and no problems with S&B. I have tried CCI BR primers and found the same thing as the Norma Diamond line in my CZ700 - S&B work without a problem, hence my belief S&B primers are much softer.
The difference in primer hardness will show a difference in the point where pressure "signs" begin to appear.

Quote:
Also Brown Dogs rifle is a AI AW......chamber is set to max headspace.....if it makes a difference.
It makes a difference.

Quote:
Only thoughts,

David.
Good thoughts.

When "we" started to hand load 150 years ago, there were no concerns about pressure - you filled the case to the top with black powder, and stuck a bullet on top.

When we started loading high pressure smokeless loads, where we could get in trouble, the only indication of "pressure" was the primer.

So it has traditionally been the thing we look at to know when we are approaching the limits.

But the reading of primers is a black art, and there are a number of variables that effect the appearance of a primer, even with the same load.

Primers are not a good indicator of pressure, but in most cases its all we have.

For a serious shooter, take a once fired case (from that rifle), and prime it. Then pop the primer with no charge in it and look at it.
You will see the edge at the pin strike is rounded and soft looking.
And the edge at the outside of the primer (the edge of the primer pocket) is rounded.
What you are seeing is the fired primer with no other effecting pressure.
This is your "base line" primer.

Now, when you look at a fired primer with a real load, any difference in appearance is due to pressure of the cartridge.

If you were take a pistol primer which has a very soft metal cup so it will fire with a blow from a 25 auto pocket pistol.
Put it in a 223 case and fire it in a Rem 700 with a 22 pound firing pin spring - it will show pressure signs at a low pressure - somewhere in the 30 to 40 Kpsia range.

In the same rifle, a Fed small rifle primer will typically show pressure in the 55 Kpsia range. The Rem 7-1/2 and the CCI 400/BR4 will show pressure signs in the 60-65 Kpsi range... all with the same spring!

Consider this. If the case pressure is 55 Kpsia (55,000), that the pressure AT the pin strike is ~165 pounds (not PSI, but real pounds). Pressure on a dome is not the same as pressure on a flat surface, so the 165 pounds is reduced. I have long forgotten my calculus (my teacher said I never learned it ;) ) but for a rough estimate, lets take a figure of 1/2.
So lets say that the pressure pushing back against the firing pin spring is ~82-ish pounds (real pounds).
Now, if the pin has a 22 pound spring, and it 0.055" diameter, the force at the pin tip is 7300 psi (and 22 pounds absolute).

It doesn't take a rocket scientist to see that the pressure in the case that is pushing to get out is higher than the pressure of the pin to keep it in.

This is where the strength of the metal in the primer cup comes in play - it is the spring AND the primer cup that holds the whole thing together. And if you change the strength of the cup, you will change the pressure point that metal starts to move out and show "signs" of pressure. But if you change the strength of the spring, you ALSO will change the pressure point that metal starts to move out and show "signs" of pressure... but the pressure is the same, it's the cup and spring that determine when you see this flow.

If you increase the spring strength, the point that the primers start showing pressure will increase accordingly.

Ideally, the spring and primer cup will be strong enough so that the only sign of pressure you will have is when the case starts to flow into the ejector hole, or extractor cuts... because the only REAL limit on pressure is the case head strength. But for the beginner, this is working too close to the edge.

David Tubb's advice on loading his match cartridge, the "6mmXC" is:

"I use the ejector marks as my pressure indicator -- when I see a shiny mark on the case head, I automatically back off the charge"

But this only works if everything else is up to peak. Sloppy firing pin holes, and weak springs will show pressure signs at ~35-40 Kpsia.

So here are the variables.

1 - Headspace. If there is space in the chamber, the primer will force the loaded round forwards to the shoulder, and the primer will protrude from the back of the case. When the powder reaches full pressure, the case will be forced back to the bolt face, and the primer (which is now stuck to the sides of the pocket under pressure) will get smushed instead of being reseated. This shows "flattening" at the outside edge, but normal appearance at the pin indentation. This will happen on the first firing of the case - after that, the case will fit the chamber, and this should not be seen again under normal circumstances.

2 - Light pin spring. If the spring is light, from age or other causes, primers will show "normal" cratering at lower pressures than they should. They will also show "shallow pin strikes", pin dents that look normal, but are not as deep as the should be. In the properly set up rifle, the primer should NOT show cratering before the case head shows shiny ejector marks.

3 - Over sized firing pin holes. If the pin hole is over sized, the cases will show cratering at low or normal pressures. These craters will have an odd look - like the top half of a donut. the outside wall of the crater will be rounded, instead of being straight and sharp.

4 - Soft primer cup. When the primer cup is soft, the case will show cratering at a lower than normal pressure. Changing the primer to one with a harder, thicker cup, will make the cratering go away, even thought the case is running the same pressure.

This is where the wives tale about "Brand X primer gives higher pressure than brand Y primer".

The pressure is the same, but the primer cups are different. You CANNOT change the pressure by changing the primer - there isn't enough compound in the primer to make a difference, or effect the pressure.

The purpose of the firing pin (other than the obvious) is to hold the pressure in the case from coming back out of the case at the primer. If it were not, we could use rebounding firing pins like auto pistols.
If the pin wasn't there, or the spring is too light, the pressure will find it's way out the back of the case through the bolt face, via the pin hole.

For a rifle that is designed for long range target/game shooting, we are working (or should be) at the limits of what is safe, but we are not letting any performance go because of sloppy or careless design or equipment.

So let's put it all together.

A solid action, minimum head space, or a case that has already been fired in that chamber.

A minimum clearance firing pin hole.

A pin spring that is strong enough to hold maximum pressures withOUT primer signs.

A primer with a cup to hold it all together.

With a rifle set up as this, the first "sigh" you will see is a shiny spot on the case.

I hope this makes sense, cuz I haven't had coffee yet.

.
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Last edited by CatShooter; 08-25-2007 at 07:04 AM.
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  #18  
Old 08-24-2007, 01:33 PM
ds ds is offline
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Thanks for all the information CatShooter, a very good thread.

If it also helps any my AI AWP and AI AWSM both have the same dims. (as best as I can measure).

Firing Pin: 0.0778" dia.

Pin Hole: 0.080 dia.

David.
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  #19  
Old 08-24-2007, 01:54 PM
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Quote:
Originally Posted by ds View Post
Thanks for all the information CatShooter, a very good thread.

If it also helps any my AI AWP and AI AWSM both have the same dims. (as best as I can measure).

Firing Pin: 0.0778" dia.

Pin Hole: 0.080 dia.

David.

Firing Pin: 0.0778" dia. Pin Hole: 0.080 dia.

You can't get any better than that. ;)

.
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  #20  
Old 08-24-2007, 03:23 PM
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i just went through primers that looked very much like the ones pictured in this post. only difference was shells that wouldn't fire once in a while. smith measured my spring and said too weak. 22 lbs. put original weight pin and 28 lb spring back in and everything looks and is working good. after reading this post i have a much better understanding between the components talked about. Cat, thank you very much for the detailed info.
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  #21  
Old 08-24-2007, 04:19 PM
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Quote:
Originally Posted by davewilson View Post
i just went through primers that looked very much like the ones pictured in this post. only difference was shells that wouldn't fire once in a while. smith measured my spring and said too weak. 22 lbs. put original weight pin and 28 lb spring back in and everything looks and is working good. after reading this post i have a much better understanding between the components talked about. Cat, thank you very much for the detailed info.
Dave... this is exactly the problem I had with my .222 Mag, 40-XBBR. It was my favorite benchrest rifle in the 70's, and I "retired" from benchrest shooting after a change in the rules made all of my rifles "Heavy varmint" class rifles, now in the "unlimited class" and not competitive anymore.

The rifle was really nice, with a big assed 2" Unertl scope on it, so I took some chisels and files, and made a nice varmint stock out of the 4"x4" railroad tie benchrest stock, and killed a bunch of crows and 'chucks with it. It was 110% reliable.

But life changed, I got married, had a rugrat, got divorced, bla bla bla... and the rifle had been cleaned up, oiled, and put away... for 30 years!

Last month, I decided to bring it back to life and whack some crows, and went out to shoot some of the original loads I had for it and sight it in. A number of rounds misfired, and the primers looked bad - cratered (EEK!!).
So I thought (mistakenly) that the rounds were somehow "bad", and tossed them... all 500 of them. In hindsight, I don't mind now, as many of the case necks were splitting from age, and I wanted to go to a newer powder (BenchMark), and a more varmint agressive bullet.

Made up new loads with brand new Remington .222 Mag brass and the starting loads were misfiring, and were cratering :(

I thought to myself... "Self, that just ain't possible, these loads are lower than standard 222 loads" :( :(

As I worked up the loads to a "reasonable" velocity, the cratering got really bad, and one of the primers blew out, just like the S&B case in the top of this thread.
It bound the bolt up, and it was tough to get open, and the bolt had to be opened by tapping out from the front of the barrel with a cleaning rod. I had never had to do this before :(

I figured that I was running about 75+ Kpsia.

But when I got the case out, there was no shiny marks or signs of pressure. I blew out the action with canned air, and the bolt slipped in like grease. I tried the fired case and it went in like a new unfired case... I think the appropriate expression is WTF ???.

Turns out that the spring took a set, and just didn't "have it" any more... and couldn't hold things together. The primer punched out, and the plug had gotten in the works, and locked up everything.

The symptoms were EXACTLY the same as a normal gun with a heavy proof load of 75-80 Kpsia, except the case wasn't at all beat up... it dropped in the chamber with no effort at all.

I replaced the spring with a new ~28# spring from a complete firing pin group that was removed from a "J lock" Rem, and all the problems disappeared at once.

I had never run into this before, and it did give me a few curious moments.

Shooting and reloading keeps you on your toes ;)

.
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Last edited by CatShooter; 08-25-2007 at 07:29 AM. Reason: Phat phingers syndrome
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