Lets say you work up a load until you start to get sticky extraction, what would the estimated pressure of that load be?
I guess another way of putting it would be, what pressure the average brass case can withstand before it loses it's elasticity or ability to relax allowing easy extraction?

There no such thing as a fix pressure then the brass get sticky. Every piece of brass in combination with the rifle its fired are different than some other brass, cartridge, rifle combination. one rifle could get a sticky bolt with normal pressure the other can be dangerously high then it get to a sticky bolt.

This source lists brass yield strength as 140 MPa -

https://www.azom.com/article.aspx?ArticleID=6380

Chamber pressure to cause brass to begin to yield can be calculated.

quote:

Originally posted by metal:
Lets say you work up a load until you start to get sticky extraction, what would the estimated pressure of that load be?
I guess another way of putting it would be, what pressure the average brass case can withstand before it loses it's elasticity or ability to relax allowing easy extraction?

T.F.M. too fucking much! need to stop way before sticky extraction. Case head flowing into ejector groove, flat primers show up way before extraction issues. YMMV

It depends on the brass maker and alloy as well as the thickness of the brass.
If you have a 55 KPSI load, a 65 KPSI overload would be hard to open the bolt.
A winter load on an older type of powder can be a "hot" load in 90 degree weather.

Chamber stretches under pressure. Brass stretches with it. Supposed to limit load peak pressure so that chamber and brass return to original dimensions after shot fired. As load peak pressure increases brass should yield before chamber does. Sticky extraction indicates brass has non-elastically deformed. Brass yield strength exceeded.

As 4sixteen above says.

However, note that because the cross-sectional area of the case just ahead of the web is typically much smaller than the area inside the case against which the pressure is pushing, and since the yield stress of the brass is only slightly higher than the maximum pressure in modern high-pressure cartridges (the yield stress of UNS C26000 cartridge brass varies between 76 and 448 mPa depending on the temper), the stress in the cartridge wall can usually exceed the yield stress.

Whether it will in fact depends on whether the steelwork around the chamber (barrel, receiver and bolt/breech block) stretches more than the elastic limit of the un-supported section of the cartridge case.

If the action doesn't flex at all (not possible, but for the purposes of argument), there would be no tensile stress in the case wall.

Keep in mind that the un-supported section of the case wall is typically very short, as the thin section of the case wall is forced against the chamber walls so tightly that it can't move, so it is really just the length of the fillet radius on the inside of the case between the face of the web and the point where final thickness is reached. Maybe just 1-2mm.

So, to sum up, stiff extraction is a sign of the action flexing (or deforming) rather than anything to do with the properties of the case.

I do not agree. If that were true, then different makes of brass would not matter, but it does.

Thick-walled pressure vessel theory. Think of chamber and barrel as open end pressure vessel. 1 end open muzzle. Other end is bolt or breech block closure.

Degree of chamber polish has a tremendous effect. I regularly have to polish the chambers of Remington magnums. Even with factory loads they will stick bolts tight. Different makes of brass and whether or not they are nickle plated also makes a difference. I have usually found that when you get distortion of case head stamping then you have gone too far.

SIMPLE TRICK FOR MONITORING PRESSURE OF YOUR RIFLE RELOADS
http://www.hodgdonreloading.co...e-your-rifle-reloads

One of the first rules of handloading is to always follow the approved reload data. The cautious reloader gradually works up to approved maximum loads to ensure his particular gun does not show pressure signs. Generally this is visual observation of the fired shell case head and primer. There is another slick way to check for pressure signs if you are interested.

Using a blade micrometer that measures in ten thousandths (.0001"), new, unfired cases can be gauged before and after firing to determine reasonably accurate maximum loads. Micrometers measuring in thousandths (.001") are insufficiently accurate to perform these measurements, and should not be used. Previously fired cases cannot be used accurately due to various levels of brass hardening. Measurement is taken just ahead of the extractor groove on the case head and must be taken at the same place on the case before and after firing. By placing a small mark on the case head – entering the cartridge in the chamber with mark at 12 o’clock – a consistently accurate measurement can be taken with each firing.

Lower pressure rounds, like the .30-30 Winchester, usually yield maximum pressures at .0003"-.0004" expansion. Modern cartridges, like the .223 Remington, will show maximum pressure at .0004"-.0005", while .308 Winchester, .270 Winchester, etc., typically yield .0005"-.0006" expansion at max pressure. Magnums, like the .300 Winchester Magnum, show maximums at .0006”-.0007” expansion, and should be measured on the belt.

In conjunction with these measurements, case head signs of pressure should be monitored as well. These signs include very flat primers, slightly cratered primers, ejector marks on the case head, and stiff extraction. All these case head signs indicate high pressure, and loads should be reduced until these signs disappear.

As always, start with the beginning load listed, and cautiously work up to the maximum shown for that set of components, using the methods listed herein.

quote:

Originally posted by dpcd:
I do not agree. If that were true, then different makes of brass would not matter, but it does.

Are you sure it's not changing pressures due to different case capacities that's causing the different extraction qualities when using different brass?

Thanks very much for the replies. I realise there are a lot of variables.
Just mainly trying to gauge approximate PSI of a load that is starting to show pressure signs.

As a guideline should be maximum pressure listed by ANSI/SAAMI Z299.4-2015 for whatever cartridge based on test chamber standard dimensions.

https://saami.org/wp-content/u...-14-Posting-Copy.pdf

Load pressure induces case, chamber and barrel stress levels. As well as bolt lug shear stress levels (bolt action rifle). Stress levels supposed to be kept below specified yield strength.

Your complicating the precess, that is a good way to have little curly ques of smoke comeing off your facial skin...

Pressure signs from case to case can vary a bunch...depending on new brass, used brass, how many times fired, and on and on..

when You get a sticky bolt, a dirty primer leak, an extractor indent on the case head, a crack as opposed to a normal boom, your over the top, cut back two grs. and call it max..If you need the pressure reading send the cases off to someone that can do that, but Ive never know anyone that did that..and it depends on the gun in question, its model, how tight is the barrel and again on and on..but 65,000 PSI is real max in some guns, but the common denominator with most reloads is 55,000 PSI in a strong bolt action, but that means nada as a matter of fact..

I think your overthinking your problem..not healthy..

Ray, I'm quite up to speed on working up loads and reading pressure signs. The reason I asked the question is relating to lots of discussion on the Gunsmithing and Custom Rifles pages on AR about Mauser metallurgy and the subject of setback.
Given that 98 Mausers were proofed in the 60K + range then if you stay under that then you are working within it's limits. That is what I've always done and never had a problem.
So the reason for the question was only to see if is was possible to put a PSI number to a hot load that is starting to show pressure signs.

Are there any places that you can send a loaded round to and they will pressure test test them?

Yes, White Laboratories at least used to. It costs $1000 per shot But you might be able to do it yourself with the piezo strain gauge test kits that are available, about which I know nothing. RSI Pressure trace is one kit.
Maybe using SAAMI specs as a guideline might be ok, but the problem is that no one has any way of knowing exactly what his pressures are unless you have the equipment, which I know of no one who does. So back to the beginning, we use primer and brass signs, which vary as to brand. Don't forget the barrel bore and groove dimensions also contribute, a factor some have missed.
It ain't rocket surgery, this reloading thing; just for those who don't want to follow some pretty well established criteria for working up loads.

Plus 1 with dpcd, spoton!

read the case, and trust your rifle,its an inity unto itself..I see no point in KNOWING the exact pressure, nor can the experts without the proper equipment that runs into some mighty big bucks,,

Such exercises are a contest in knowledge, I know more than you and I can baffle you with BS type of controversial conversations can support the old saying that "A little knowledge is a dangerous thing"...

Ray , calm your farm, I didn’t come down in the last shower. The original question was answered and some good ideas put forward.
It probably comes down to the yield strength of the brass case plus a lot of variables which I acknowledged.
There is no answer and I’m happy with that. I’m off now to blow myself up with some hot loads.

I think farm might be an insult to Ray, metal. What have you got that rhymes with ranch?

Ha ha yes you’re right but he’s probably out the bush for a while and hopefully when he gets back he won’t be so cranky.

I went through this and had to go see a therapist!

I finally settled on some sensible simple thumb rules.

1. NEVER try to get above maximum velocity
2. The bolt face and ejector hole will start shaving brass first before you get hard extraction.
3. Primer flattening is not easy to detect. But hat brim on extracted primers is a sure sign of high pressure.
4. By the time you get hard extraction, flattened primers (not always a pressure issue) etc. your pressure is probably over 70,000 PSI.
5. If you are having to trim cases more than 3 or 4 firings, then you are above max pressure.


JMHO

If you already know that you are seeing pressure signs, then you are above 60,000 psi and probably more like 70,000 psi.

Why the risk?

quote:

Originally posted by metal:
Thanks very much for the replies. I realise there are a lot of variables.
Just mainly trying to gauge approximate PSI of a load that is starting to show pressure signs.

Naki, I never said I was running that hot, it was a hypothetical question. I probably didn't make that clear. I AM NOT A HOTRODDER.
I figured it would be in that 60-70K range when brass starts to flow, or maybe more.
I thought there might have been a ballpark PSI number for it generally but it seems not.

No offense intended mate. I thought you were already seeing pressure signs.

I learned the hard way developing loads in modern rifles 25 years ago for 6.5X55 & 280 AI in the days when reliable load data was not available.

I used to measure case head expansion of every reload - about 200+ in each caliber. Made up my own little wooden inserts for the micrometer to make sure every case was measured at exactly the same spot. Not the kind of thing I ever heard of anyone doing.

I ended up with about 5 to 8 cases in a lot of 50 that had varying levels of loose primer pockets.

I started measuring the used primers! Another trick you do not read about.

20 years later my own safe loads were validated by published data!

quote:

Originally posted by metal:
Naki, I never said I was running that hot, it was a hypothetical question. I probably didn't make that clear. I AM NOT A HOTRODDER.
I figured it would be in that 60-70K range when brass starts to flow, or maybe more.
I thought there might have been a ballpark PSI number for it generally but it seems not.

No offence taken, translating ideas to words on forums can sometimes get messy.

Metal,
My posts were not directed at you, but at the conversations on some internet blogs, wherein they become out of touch with reality.....Sorry you got your shorts in a wad, it wasn't my intention!! I apoligise for that.

Ha ha shorts in a wad, I love it. Not pissed at all, I knew you meant well.

From Olin Brass - modulus of elasticity- Cartridge Brass-
Material is 70 copper/30 zinc with trace amounts of lead & iron , called C26000. Material starts to yield at 15,000 PSI when soft (annealed), and 63,000 PSI when hard.
Material yields, but continues to get stronger up to 47,000 PSI when soft, and 76,000 PSI
when work hardened. Modulus of Elasticity is 16,000,000 PSI. This means to pull a 1.000 inch long strip to 1.001 inch long induces a 16,000 PSI stress.
So if you pull a 1.000 inch strip to 1.005 inch long, you get about 76,000 PSI, which is the max obtainable.

Thick-walled cylinder pressure vessel which a rifle can be modeled as internal pressure induces cylinder wall stresses and strains. Case or chamber stress levels are multiples of load pressure. Hoop stress, highest of induced stresses, is a function of chamber pressure and chamber inner/outer diameters.

Did the calcs for one of my rifles maximum chamber hoop stress is about 1.4x peak chamber pressure.

Great info thanks.

"read brass for pressure signs" ..
wow, what a can of worms - I thought I had this down, till i fired some factory 270, 300wm, and 308 ...

i look at my primers first - i really want there to be some rounded edge on them for my reloads ..

then factory 270 and 300wm, in "Stock" guns resulted in primers WAY flatter than I allow my reloads. this also happens in some 308s...

but I am an old reloader, not a bold one.. if i need that extra 200fps, i get a bigger caliber

quote:

Originally posted by 243winxb:
,,,,So if you pull a 1.000 inch strip to 1.005 inch long, you get about 76,000 PSI, which is the max obtainable.

not even CLOSE . though it is the max sustainable! one COULD detonate a rifle with a 100k or 150k psi situation .. it's not repeatable, but the upper limit of what is OBTAINABLE isn't defined by brass failure .. we've all seen pictures of steel rain

Go to the SAAMI website and look up the PROOF LOAD PSI pressures. Makes scrap brass in 1 firing.

Many modern cartridges have a working pressure of 65,000 PSI.

Repeated reloading/firings of the same brass will cause primer pockets to become loose at higher pressures .

If pockets become loose in 5 firing or less, reduce the powder charge. Your over pressure.

Avoid sticky extraction on a regular bases. Its a true pressure sign.

"Proof cartridges are designed to stress firearms components which contain the cartridge in order to assure safety in the recommended use of the firearm during its service life."

p.351 - https://saami.org/wp-content/u...-14-Posting-Copy.pdf

About 1.4x maximum pressure (per SAAMI voluntary performance standards) similar to strength testing pressure vessels and piping fabricated to code requirements for industrial use.

quote:

Originally posted by 243winxb:
Go to the SAAMI website and look up the PROOF LOAD PSI pressures.

SAAMI doesn't REQUIRE proofloads, only CIP

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