Pressure signs ?

I have found "case life" to be the most reliable indicator of excess pressure.

If I can load a case 8-10 times, my pressure is good. If primer pockets start enlarging after 2-3 reloads, my pressure is too high., Case head expansion is also as decent indicator. (assuming you're using quality brass in a SAAMI spec chamber.)
 
Ben Dover said:
I have found "case life" to be the most reliable indicator of excess pressure.

If I can load a case 8-10 times, my pressure is good. If primer pockets start enlarging after 2-3 reloads, my pressure is too high., Case head expansion is also as decent indicator. (assuming you're using quality brass in a SAAMI spec chamber.)
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Yes, long case life is a good safe pressure indicator.

If there's less than a. 002" spread in case headspace between fired and resized case headspace. Some have got over 50 reloads per 308 Win case doing this.
 
44 AMP, have you ever shot rifle proof loads generating 81,000 psi?
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No. But I have fired a round that at best estimate generated between 90-110,000 psi. I don't recommend it.

Traditional pressure signs don't show up until you are at 70,000 PSI, which is well over a max load. You could be over the max pressure allowed for the cartridge and still not get any of the traditional pressure signs.

That is unreliable.
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What "traditional" signs are those? Cratered primers? Flattened primers? Pierced primers? case head expansion beyond initial .001"? something else?

Those things can, and have shown up at pressures below 70k psi, and under the right conditions can show up below regular working pressures. And as you noted some don't show up at much higher than working pressures.

I think what is unreliable is the expectation that a certain pressure sign will ALWAYS show up at XXXX psi and that a certain pressure sign showing up ALWAYS means you have XXXX psi (or more).

Most of us consider cratered primers to be a pressure sign. They are. But while often a sign of pressure higher than desired they can also happen at normal pressures, because of factors specific to individual guns and/or ammo components.

Perhaps its just the way we use language differently. I consider pressure signs reliable in the sense that when you get them, you got them, and getting them means something isn't what we want it to be.

They are not reliable predictors of anything else, though. Nor do they show up on a "set schedule". Every gun can be different. Every individual round can be different, despite all we do striving for uniformity.

I've seen the same ammo behave normally in all aspects in one gun and crater primers in another.

All our measurements have tolerances and sometimes you get performance at either end of the bell curve when you expect something in the middle.

Not getting what you expect doesn't always mean the thing is unreliable, but it could mean your expectations might be.
 
44AMP said:
I disagree. The marks are very reliable, they are there, you can see them.
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jmr40 said:
Traditional pressure signs don't show up until you are at 70,000 PSI,…
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I should have put up a link to the article. What is remarkable is Bramwell demonstrates in one brass lot with matching load histories and fired in the same gun, one case gets a specific pressure sign with a powder charge producing just 40,000 psi peak pressure, while another case in the same lot doesn't get that exact same sign until it is loaded to 70,000 psi. So that raises the question, which of the two loads is that pressure sign telling you is the limit? I think this is the problem that caused the old pressure-sign-based load manual data to include a few loads that were too hot in some guns.

The conclusion I took from the article is the common practice of incrementing loads until you find the first case or primer to show a clear pressure sign and then backing the charge off 5% and loading and firing without further investigation is something of a crapshoot. Just like shooting groups, you actually need to get pressure signs in a big enough sample of cases (I would use at least 10, but 30 is better) and then to choose a load based on an acceptable brass loss rate (percent of the population outside the bottom end of the pressure sign bell curve based on the SD of the powder charges producing the sign). The pressure sign in one case or primer is, obviously, valid for that particular case or primer. The problem is knowing how far you can extrapolate the result from one case to others. Was that case with the sign exceptionally resistant to pressure or average or below average? You have to run the test ladder repeatedly to find where the darn things fall.


reynolds357 said:
Despite it sounding crazy, seating closer to lands increases pressure.
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It depends how deeply you seat. Here's a curve derived from data in Dr. Lloyd Brownell's 1965 U of M study of pressure for DuPont. It is for a round nose bullet, which makes the curve more gradual than a spire point does, but it gives you a good look at the shift and the fact there is a minimum pressure seating depth either below or above which pressure is higher. Above the minimum pressure seating depth and closer to the lands, loss of gas bypass is the dominant term. Deeper than the minimum pressure seating depth, the bullet intrusion into the case shrinking the powder space becomes the dominant term.

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Today I shot ten rounds of each of these loads over the MagnetoSpeed. The heavier load definitely exhibited better accuracy. The interesting part is that the MV is identical to the original load even though it's .9 gr more powder. It also didn't seem to exhibit any more increase in effort to lift the bolt than the lower charge. I also measured the case length on the fired rounds and compared to full length sized cases they averaged .003"-.006" longer. This is for both charges. As far as case life, with the original charge I have fired at least 600+ rounds using the same 100 cases and the primer pockets all still pass a go-no go gauge no problem. One other interesting thing, this charge is only .1gr heavier than the load I shoot in my AR10. The difference is the AR10 ammunition is loaded quite a bit further into the case in order to fit in the magazine, but it's also using Nosler brass which is a little larger case capacity and I believe also a harder brass.
 
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one case gets a specific pressure sign with a powder charge producing just 40,000 psi peak pressure, while another case in the same lot doesn't get that exact same sign until it is loaded to 70,000 psi. So that raises the question, which of the two loads is that pressure sign telling you is the limit?
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This is my point, NEITHER is telling you the limit. All both tell you is that something is going on that isn't going on when you don't see pressure signs, so its up to you to figure out what is going on, and if it is at dangerous, or just undesirable levels.

Think of it as the "check engine" idiot light (do they still call them idiot lights? :rolleyes:) It tells you SOMETHING is going on, but it doesn't tell you if it's an oxygen sensor or your gas cap isn't tight, or if you're having something serious happen.

You've got to figure that out from other things.
 
Bart B. said:
What's the primer cup edge radius minimum that is the standard to define a flattened primer?

Is it the same for all primers regardless of cup metal properties and dimensions?

I've shot 7.62 NATO proof loads at about 81,000 psi (67,500 cup) and most people looking at the fired case heads and primers say they're a normal maximum load.
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Sounds like we are going to need a new hand tool to measure primer cup edge radius! :D
 
You can call it a fix or an on going adjustment.

You could say the same for originally finding the lands and determine what jump works best.

Its a valid method to extend the use you get out of a barrel.

note: it my view as to why a rifle that you can easily replace the barrel on is a very good idea for a gun that is shot a lot and or a caliber that is somewhat short of barrel life.
 
As a comparison to the comment I made about 6.5's flattened primers, and the ejector swipe marks, is when I load some "stout" .308 155.5 gr SMK "Palma" Varget loads for my Savage 12 F-TR . I was at about 2990 fps and never really observed substantial flattened primers or ejector swipes (and I was running FC brass). I did see slightly flattened primers but per my notes spent casing extraction was normal. The general concensus is that when you observe ejector swipes your starting to get into high pressure territory. Someone needs to invent a ported pressure gauge that screws into your barrel and gives you a black and white CUP number pressure !
 
Road_Clam said:
Someone needs to invent a ported pressure gauge that screws into your barrel and gives you a black and white CUP number pressure !
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There's drawings and specs in this SAAMI document. Section III has all the details.

https://saami.org/wp-content/upload...99.4-CFR-Approved-2015-12-14-Posting-Copy.pdf

An electronic transducer reading actual press per square inch would be easier and faster and you wouldn't have to mess with and measure all those little copper disk's thickness and not loose their tarage table.
 
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I am planning on a new barrel, that's why I put the gun away for the last 9 months. I can't afford it right now, got laid off last spring and started a new business in September so cash is tight. But I got a break for the last week due to a holdup on my current project and was bored so I dug the rifle out, remeasured the chamber and since there was still plenty of the bullets bearing surface being seated in the neck, I figured what the heck and adjusted the load to compensate for the added space in the case. Bingo, am getting the same velocity and the same accuracy I was originally getting and maybe can get another 1000 rounds through before scrapping the barrel. Meanwhile, saving my pennies so maybe by next summer a new barrel will be installed. The longer length isn't an issue since I single feed them anyway.
 
Road Clam said:
Someone needs to invent a ported pressure gauge that screws into your barrel and gives you a black and white CUP number pressure !
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Then you'd have to have a port in the barrel. Why bother when you can just glue on a strain gauge. Bramwell has shown they are actually more repeatable than either copper crushers (poorest repeatability) or piezoelectric transducers (in the middle). You can buy the bluetooth version of an instrument for measuring those and take it to the range. I have the older serial port version and it works just fine.
 
I am planning on a new barrel, that's why I put the gun away for the last 9 months. I can't afford it right now, got laid off last spring and started a new business in September so cash is tight. But I got a break for the last week due to a holdup on my current project and was bored so I dug the rifle out, remeasured the chamber and since there was still plenty of the bullets bearing surface being seated in the neck, I figured what the heck and adjusted the load to compensate for the added space in the case. Bingo, am getting the same velocity and the same accuracy I was originally getting and maybe can get another 1000 rounds through before scrapping the barrel. Meanwhile, saving my pennies so maybe by next summer a new barrel will be installed. The longer length isn't an issue since I single feed them anyway.
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Frankly I would keep moving it up as needed until there is no more throat to work with. Keep having fun and maximize the barrel life.

New barrel get short throated and gives you even more to work with.
 
Don Fischer said: "I've shot 7.62 NATO proof loads at about 81,000 psi (67,500 cup)...."

I don't wish to highjack the thread but I'm interested if that conversion from psi to cup was already listed or if there was a formula to do the calculation.

I have two: One is "ansi" and the other "EuropeCIP"

Ansi: PSI = CUP x1.516 - 17902 CUP= 17902 + PSI/1.516

From your CUP figure of 67,500 the PSI comes out to 84,428
From the PSI of 81,000 the CUP comes out to 65,239

EuropeCIP: PSI= (CUP + 1.220911) - 2806.88 CUP= 2806.88 +PSI/1.20911

From your CUP of 67,500 the PSI comes out to 78,808
From PSI 81,000, CUP = 69,313

There is a notation that EuropeCIP is accurate for rifles, not handguns
 
I agree RC20, I guess that's the plan. It should last quite a while since I'll probably only put 20-40 rounds a month through it during the winter months. Summer months not so much, other hobbies for summer.
 
jetinteriorguy
Sounds like your loads are working out. Glad to hear it! Your adjustment of bullet seating depth with a slight bump in powder gave you some renewed life for the rifle. That is great!

It does seem like your thread got hijacked a bit, no?
 
cdoc42 said:
Don Fischer said: "I've shot 7.62 NATO proof loads at about 81,000 psi (67,500 cup)...."

I don't wish to highjack the thread but I'm interested if that conversion from psi to cup was already listed or if there was a formula to do the calculation.

I have two: One is "ansi" and the other "EuropeCIP"

Ansi: PSI = CUP x1.516 - 17902 CUP= 17902 + PSI/1.516

From your CUP figure of 67,500 the PSI comes out to 84,428
From the PSI of 81,000 the CUP comes out to 65,239

EuropeCIP: PSI= (CUP + 1.220911) - 2806.88 CUP= 2806.88 +PSI/1.20911

From your CUP of 67,500 the PSI comes out to 78,808
From PSI 81,000, CUP = 69,313

There is a notation that EuropeCIP is accurate for rifles, not handguns
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Don't know where you got that from. I've never shot a proof load in my life!
 
Well like most threads, it's just evolved into another discussion. Funny, I usually learn something from whatever discussion that happens in threads. I just avoid getting dragged into any negative junk.
 
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