Pressure Signs vs Pressure

[steve4102]

Has anyone ever done pressure testing to determine at what pressures the most looked for pressures signs actually occur?

For example, stiff bolt lift, is there any test data that shows at what pressures the case expands enough to cause the bolt to be stiff? How about loose primer pockets, any idea at what pressures a round is running at to get loose primer pockets after a few firings?

Thanks

[rmorgan9718]

any accurate measurement would have to be done by someone with pressure chamber or CUP devices. If you follow commercial load data, you are assuming that their pressure curves are accurate and precise. Chronograph info would be barrel/chamber/shell/bullet dependent, but that might give you more insight into your specific firearm.

rick

[Creeper]

To deviate from the current thought... Pressure alone is not necessarily the cause of common case issues/failures.

Cases that are repeatedly full length resized and/or fired in a axially loose spec chamber will cause a case to stretch. Once a case stretches excessively, it is weakened and will stretch again with even less pressure than previously applied.
This is why cases that are neck sized or neck sized and "shoulder bumped" only will last much longer than full length sized cases... far less "working" of the brass. Not to mention, accuracy is frequently improved... but that's out of context with your inquiry.
Of course, full length sizing does have it's place, but in a bolt action rifle used for target/recreational shooting, there is no need for it.

If you must full length resize, may I suggest you send a new, once fired case to one of the custom sizing die makers such as Neil Jones.

Individual case lots can have primer pockets that are on the high side of the tolerance to begin with... combine that with primers on the low side, and you have a loose fit right out of the box.
Going back to the rifles chamber... a chamber that is on the large end of the specification radially, and in particular at the chamber base diameter can be a cause for loose primer pockets. A full length resized case should be less than .002" and preferably less than .001" in OD, as compared to the matching ID location in the chamber.

To give you one example of why I'm discussing these elements rather than "excessive pressure" as the primary cause of case stretch and primer pocket looseness...
A handloaded 6PPC (or other) benchrest cartridge in a custom fit, "tight neck" chamber is frequently shot "hot". Benchrest competitors do not care about a little over pressure, they only care that all 5 shots go into the same hole on the record target.
Benchresters typically will neck size only... just sufficient to hold the bullet in place. Some may neck size and shoulder bump .0005" to .0015" to reduce bolt lift drag. The small quantity (20-30) of perfect, "record" cases may be used well in excess of 100 times in a season... and may be only replaced when the barrel is replaced.
Because there is little to no radial case expansion, primer pockets seldom get excessively loose even with hot loads. Of course, the vast majority of competitors use extremely consistent, premium brass made by Lapua and Norma as well as match grade, usually Federal, primers.

So... other things to think about besides pressure.

Cheers,
C

[browninghunter86]

not tryin to steal thread but CREEPER it is amazing how many on forums say vice versa is true--FL sizing making brass last longer and better accuracy. I do not have alot of reloading experience or competition shooting so I can not say one way or the other.

[243winxb]

deleted

[Creeper]

not tryin to steal thread but CREEPER it is amazing how many on forums say vice versa is true--FL sizing making brass last longer and better accuracy. I do not have alot of reloading experience or competition shooting so I can not say one way or the other.

Hi browninghunter86...

Think of it in these terms. You take a "new" case... say .308 as an example. SAAMI minimum spec for a case length at the datum is 1.627". Maximum chamber spec is 1.640". That's a potential .013" stretch from case head to center of the shoulder.
Squeeze it down, now fire form it out, now squeeze it down... repeat as often as necessary for incipient case head separation.

No one I know of, in 20 years of benchrest competition, used a production FL resizing die in a competition rifle... except for those that used custom FL dies, cut to match a once fired case in a custom chamber.
Not saying that some rifles aren't more accurate using FL resizing... just saying that for people who's goal is to reuse the cases they worked long and hard on, making each case identical in weight and dimension to the tenth of a grain and .0005" or less dimensionally for an entire season of competition, and to shoot all bullets into, literally, the same hole... FL dies are not used except in the previously mentioned conditions.

Certainly, you use FL dies with a semi-automatic rifle, and certainly you use FL dies with hunting rifles... but there is absolutely no need to use them in a recreational or target bolt action rifle... unless you have one of those rare rifles that somehow prefers FL sized ammunition, laying there in the bottom of the chamber, rather than ammunition perfectly sized and completely concentric to the chamber as one can make it.

Is my position arguable? Most certainly... but preferably from an objective and broadly sampled view rather than from anecdotal evidence.
Could I be wrong? Certainly... anyone is invited to prove me so. I am more than willing to listen to what someone has to say.

browninghunter86, please... do not take my word for it. All I ask of you is to research the information available to you, provided by people with known reputations. Competition shooters, experienced professional gun writers/experimenters/handloaders, custom die makers and even production die makers.

Cheers,
C

[browninghunter86]

Creeper good info. That is what I was just thinking that FL sizer users most likely have very expensive dies custom made to their chambers and tools they used to make their barrel. I have a Shilen Match barrel that is shooting pretty good thus far. I like the Collet Die not needing lube and is alot easier to set up and use. I have some groups I shot so far with the new barrel posted and looks promissing

[Creeper]

Shilen makes a nice barrel. I shot the 2nd smallest 100 yd. record group I've ever shot with a Shilen.
I don't know what caliber(s) you're working with, but when you get a chance, go to Sinclair International and look at Wilson hand dies and Forster bushing bump dies. Also go to the previously mentioned Neil Jones website and take a look at the custom dies he makes.

And if you aren't already using them, get some Lapua or Norma brass.

Cheers,
C

[Bart B.]

Creeper mentions:

No one I know of, in 20 years of benchrest competition, used a production FL resizing die in a competition rifle... except for those that used custom FL dies, cut to match a once fired case in a custom chamber.
Not saying that some rifles aren't more accurate using FL resizing... just saying that for people who's goal is to reuse the cases they worked long and hard on, making each case identical in weight and dimension to the tenth of a grain and .0005" or less dimensionally for an entire season of competition, and to shoot all bullets into, literally, the same hole... FL dies are not used except in the previously mentioned conditions.

There are centerfire rifle cartridge shooters out there who full length size their fired cases with regular production dies and shoot groups just as accurate as those in the benchrest discipline. Some of them have shot 10-shot groups 40 years ago using Winchester 70's smaller that current benchrest records. They've used standard full length sizing dies but lapped out their necks to a bit smaller than a loaded round's neck diameter so as to not need an expander ball. And in a SAAMI spec chamber, too.

Sierra Bullets' been using commercially available full length sizing dies on their fired cases used to test bullets for accuracy since the 1950's. Nobody shoots 'em any more accurate than they do. Nowadays, they use Redding Full Bushing dies when possible, otherwise Redding standard full length sizing dies. Their test barrel's chambes are SAAMI spec or close enough to not matter; none are tight necked ones. At 200 yards, their best match bullets stay under 1/4 MOA; same as what benchresters use. I've seen some of their 10-shot test targets with 30 caliber bullets measuring in the 1/8 MOA range. . . .metered powder charges in full length sized cases.

There's folks who get 50+ reloads on a .308 Win. case full length sizing it. But they're smart enough to not set the fired case shoulder back more than a couple thousandths. And they don't use chamber headspace 13/1000ths greater than a new case headspace has. And it doesn't matter whole lot how much smaller the case body is than the chamber body 'cause bottleneck cases headspacing on their shoulder center perfectly up front in the chamber when they're fired anyway. Doesn't matter how much clearance their is around the case neck to the chamber neck; they center perfectly. Folks not believing nor understanding why need go do some measurements and observations on botttleneck case and chamber design as well as what happens when the firing pin strikes the primer. In fact, full length sized cases do a more consistant job of centering up front than neck sized ones.

And all these wonderful feats of accuracy equalling and bettering what the benchresters get is done with sloppier case weight and dimension tolerances than 1/10th grain and 5/10,000ths inch. 2 grains and 2/1000ths is good enough in box magazine repeating rifles to equal benchrest performance in single shot rifles.

Here's a repeat of two age old myths:

unless you have one of those rare rifles that somehow prefers FL sized ammunition, laying there in the bottom of the chamber, rather than ammunition perfectly (neck) sized and completely concentric to the chamber as one can make it.

Anyone believing a full length sized bottleneck case lays in the bottom of the chamber or a neck sized case is perfectly concentric with the chamber is totally ignorant of reality. If they ever learn and understand what forces are applied to that round, both as it's resting in the chamber as well as when its fired, they just might change their mind.

[Creeper]

Thanks for sharing your information Bart.

Cheers,
C

[Bart B.]

Creeper, I didn't think you would believe what high power match rifle winners and record setters have known for decades; the basis for most of my comments. Having been one of them as well as classified in the top 2% of scores fired, we well know the mind set of most benchresters. Sierra Bullets' track record with full length sized cases may not be believable to you, either.

It may not matter that proper full length sizing's the way high power folks equal the accuracy benchresters do with their neck sizing, but it's a fact of life. Go to the NRA's web site National Records pages, find the names most frequently and you'll see Tubb, Tompkins, Gallagher and virtually all others who've been using full length sized cases for decades. Their full length sized cases shoot just as accurate as (sometimes better than) neck only sized ones. I've shot with them often over the years; sometimes beating them. We've shot brand new cases putting bullets closer together at long range testing rifles and ammo for accuracy than a lot of benchrest records have.

Yes, your position's arguable (debatable?). But by the implication of your response, not from an objective and broadly sampled view rather than from anecdotal evidence. You may well be more than willing to listen to what someone has to say, but seems to me you won't believe it.

But the first thing you've gotta learn is tha full length sized cases do not rest on the chamber bottom when they're fired; most of them ain't there berore the firing pin even starts forward. I'll be glad to help you understand.

[Creeper]

Hi Bart,

I’m afraid I don’t have the energy to argue with you. It is a waste of the limited time and energy I have available.

The hostility and pointed aggression in your language and tone leads me to believe that there would be no reasonable exchange of ideas… but rather a point-counterpoint confrontation. I have learned through experience to avoid internet verbal combat... as a positive, respectful outcome is rarely the result.

I’ve stated my views... and you yours. I don't feel the need to defend myself, or convince anyone of anything.
I think that those who read our respective posts are intelligent enough to take from them what they will... and make their own choices.
As my comments are fairly concise... I have nothing to add that one could not easily find on their own, should they choose.

Best wishes to you Bart, and again, thank you for sharing in this thread.

Cheers,
C

[243winxb]

Steve4102, SAAMI lists maximum pressure for Proof Loads. Its different for each caliber. They have a warning that the brass has to be destroyed after firing. This might give you an idea. Go to last page of PDF & work up. http://www.saami.org/specifications_...wnload/206.pdf 93,000 PSI is the highest. Not much help, i know.

[Bart B.]

Steve4102 asks:

Has anyone ever done pressure testing to determine at what pressures the most looked for pressures signs actually occur?

Well, sort of.

Some years ago I was shooting Lake City Arsenal M60 proof loads in 7.62 NATO chambered M1 Garands. The load was an LC-65 case weighing 180 grains, FA-956 primer, 41 grains of IMR4475 (very similar to IMR3031, but much cleaner burning) and a 173-gr. FMJBT bullet. In Lake City's proof test barrels, it produced 67,500 CUP (about 84,000 PSI). After firing a dozen of them, the cases didn't show any imprint of the holes in the bolt face for ejector and extractors to fit in. That same set of components in a new Federal brass .308 Win. case of 170 grains weight fired in the same chamber had very visible imprints of the bolt face holes in their heads. That same LC-65 case, powder charge and primer normally had a 148-gr. FMJBT bullet in it as the standard M80 service round producing 50,000 CUP (about 57,900 PSI)

Which tells me the Federal case brass was softer than the LC brass. And harder brass will have less peak pressure signs than softer brass.

Same thing with primers; those with soft or thin extrude more around the firing pin into its hole in the bolt face with the same amount of pressure.

In my opinion, estimating peak pressure from visible signs, or measurements, on fired cases is not going to be very accurate.

A bolt that's hard to lift may have its face way out of square. Cases fired in chambers tend to have their heads flattened out closely matching the bolt face angle. Sizing those cases doesn't square up their heads. Firing a case from such a condition will sometimes bind the bolt when the high points of the case head and bolt face align with each other. Even with normal safe peak pressures with fired cases partially neck sized with a full length sizing die, this happens and is often believed to be caused by peak pressures bing too high.

[Clark]

steve4102

Has anyone ever done pressure testing to determine at what pressures the most looked for pressures signs actually occur?

For example, stiff bolt lift, is there any test data that shows at what pressures the case expands enough to cause the bolt to be stiff? How about loose primer pockets, any idea at what pressures a round is running at to get loose primer pockets after a few firings?

Staying inside the world of Quickload predictions, I can predict what load is at the threshold of loose primer pockets.

The 1889 Mauser case head built with a large primer pocket is common to cartridges I have overload worked up to the threshold of loose primer pockets: 243, 257RAI, 260, 270, 308, 30-06, and 8x57mm.

I have rifles, but have not done it in 22-250, 250 Sav, 6.5x55, 7x57, 300Sav, and 35W. I expect that I could predict the threshold of loose primer pockets in these cartridges within 2% powder charge. That assumes that I have used that jug of powder in another cartridge where I knew the threshold. That also assumes I have the feed back of a lower pressure round that the chrono velocity matched the QL predicted velocity.

a) For an individual hand loader of a 45 Colt revolvers with thin chamber walls, we care what the pressure is relative to what pressure that revolver is known to tolerate.
b) For selling 308 ammo, we care what the pressure is and how that relates to how the 308 was SAAMI registered.
c) But for an individual hand loader of 308 ammo for his strong rifle, the pressure does not matter. The threshold of the effects of pressure are what matters.

That third case is where the QL predictions are useful to speed up load development. The system is precise, but not accurate. At least we cannot trace the accuracy to the NIST, so the accuracy is as meaningless.

Today I made a sound peak detector for guns. I am working in miliVolts not db re ubar. All I need is precision [not accuracy] to plot the SPL and find the inflection point for the threshold of super sonic gas escapement.

[impalacustom]

Hmm I'm going to have to disagree with you Creeper. You must not have shot on the bench in a long time, a lot of the shooters use a FL die with a neck bushing. Fire a round, read your headspace, set up the die to push the shoulder back 1-2 thousands, set neck tension to 1-2 thousands, and shoot. If you don't eventually FL size you will find you will have a very hard time loading and extracting your cartridge after about the 5th go, give or take a few.

[243winxb]

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[Bart B.]

Impalacustom, it's not a case sizing issue regarding Creeper's stance that baffles me the most, but how in the dickens does his neck only sized cases "float" in a chamber perfectly centered if the same forces of gravity pulls a full length sized case down to the bottom of it? Maybe he puts hydrogen or helium in the cases along with powder so they float in space like a balloon so there'll be a narrow space all the way around the case body.

Clark, does Quickload have allowances for the bore and groove cross section area in the bore vs the bullets? SAAMI specs have a standard for that; with the .308 Win. it's .0736 square inch.

[mehavey]

does Quickload have allowances for the bore and groove cross section...?

Actually, ...yes.



As to "floating" for an FL, vs centering for a NS -- I make the assumption that the NS'd cases still retain (near) full chamber wall dimensions as opposed to the FL'd smaller/sized wall dimensions. Hence the NS case has less radial "rattle" space when seated.

Of course this is only works when the bore is exactly concentric to the chamber. If not, then a little "float" is useful to center-up the case neck when chambered.

[mehavey]

As to the OP's original question.... pressure vs pressure signs... it depends.

Soft brass (Federal) will start flowing/extruding into the extractor cut-out much earlier that Starline/Winchester. Ditto primer pocket expansion as the case head expands beyond design levels. Worse, these two phenomenons occur at different pressure levels and for different brass.

I find my AR's primer pockets get loose after a half-dozen firings if I'm consistently loading much above 55,000psi (by Quickload/chronograph comparisons using Winchester brass). Brass will begin to actually/immediately flow at about 70-73,000psi. (Lapua/Starline brass will last just a tad longer/higher.)

But my Swift is different; my 243 is different; my`06 is different, my 300WinMag is different.... you get the picture. And each is different w/ different brand brass -- and between significantly different production year lots.

[steve4102]

Brass will begin to actually/immediately flow at about 70-73,000psi. (Lapua/Starline brass will last just a tad longer/higher.)

OK, this is the kind of stuff I am looking for. How do we know this and is there any published data to confirm?

Thanks.

[Bart B.]

mehavey, thanks for the screen shot of Quickload's bore/groove area input. That certainly effects pressure slope and peak numbers. But so does bullet jacket hardness as well as the chamber's leade angle; they're not all that easy for consumers to determine and that may be why these two pressure-changing elements ain't part of Quickload. But Quickload's probably the best thing out there to get a reasonably accurate answer. Too bad Oehler quit selling their pressure measuring systems; at least I think they did.

Regarding rimless bottleneck case fit in chambers after the bolt closed on them. They all rest on the chamber bottom (gravity?) when pushed into the chamber and the bolt's still open as there's no external force changing that. All of 'em (new, fired, or resized any way), after the bolt's closed have their back ends pressed against the chamber wall (typically at the pressure ring) by the extractor. If it's a sliding one in front of a locking lug as in a push-feed Model 70, it pushes the case up stopping against the top of the chamber (there's space between the bottom of the case body and chamber wall). Mauser style external extractors push the case head to the opposite side; left on a Win. 70 classic controlled feed right hand bolt. Up front at the shoulder, in-line ejectors in the bolt face push the round forward until its shoulder centers in the chamber shoulder centering it very well. And that well centers the case neck in the chamber neck. Even a .243 Win. round's neck is perfectly centered in .308 Win. chamber this way. With bolts having external ejectors, the back end of the case may be anywhere depending on several things. In either instance, when the firing pin smacks the primer, that drives the case forward hard into the chamber shoulder centering the round very well in the chamber up front. There's no "rattle space with either one; both are held very repeatable in centering up front. Neck only sized cases whose body diameters have grown where they interfere with the chamber walls can force the case neck off center in the chamber neck; 'tain't no such thing as perfectly round cases and chambers; cases are the worst of them.

In my measurements of case neck centering on case shoulders after sizing, I tried Neil Jones' neck/shoulder bushings set to size neck almost to the shoulder as well as bumping the shoulder back a thousandths. And also full length sizing them (in dies with necks lapped out a couple thousandths smaller than a loaded round's neck diameter) setting the shoulder back a thousandth or two. In all instances, full length sizing .308 Win. and 30 caliber magnum cases, necks were better centered on case shoulders when full length sized. I attribute that to a full length die holding the fired case body repeatably as the shoulder's set back while sizing the neck down.

[Bart B.]

Steve, if you want to know what pressure is for different loads in your rifles, there's a company in Arizona that does that for you:

http://www.arizonaammunition.net/Pro...20Services.htm

While it ain't cheap and requires you to send both rifles and ammo to them, it may be worth the expense to know reliably what your ammo's pressure is in your rifles.

Otherwise, someone may have an Ohler 43 system you could buy then do your own presure tests.

[old roper]

There is always different between custom rifles vs factory and how short yardage BR load vs other types match rifles.

Short yard BR that shoot the 6ppc load at the range vs the others that pre load. I shot the short yardage and we used neck dies with bushing and this was long before Redding and the others got into making bushing dies. Wilson been making bushing dies think it over 80 years and Wilson made FL die for the arbor press at one time. http://lewilson.com/home.html


CHE (Case Head Expansion)

http://www.varmintal.com/arelo.htm#CaseHead

Just type in "case head expansion" and do a search and you will find more post on that

[Brian Pfleuger]

Steve, if you're thinking of using this information to "push the limits", there's a much more reliable, safer (relatively) and fairly inexpensive way to do it than eyeballs and micrometers.

RSI Pressure Trace

Pushing the limits of pressure is not very productive. As an example, using a 150gr Hornady A-Max in 30-06 with a 24" barrel, QuickLoad gives 3,162fps at 73,300psi and 2,988fps at 59,900psi with a max load of H380.

In other words, you get a 5% velocity increase for a 22% pressure increase.

If you're just wondering in case you run into these things in load work up, I wouldn't be concerned about reaching these numbers. If you stay in book limits and do what you're supposed to do, you'll know there's trouble before you get these kinds of pressures.

A chrongraph to check velocity against expectations would go a long ways too.