Primer protrusion

[alinwa]

Is "6.63 NATO" a typo?

Yeahh, me and numbers. I'm an idiot with numbers. I meant 7.62

The subject was cartridges that exhibit primer protusion when pressures should be adequate to force the casehead back to the breechface, the only serious testing on this I've seen quoted is Ackley's test of the .30-30.
If you are getting this sort of protrusion with other cartridges I'd like to hear more about that. It happens to ANY cartridge! I guess this is our first breakthrough. There's nothing magical about the 30-30, PO used it because it was easy and he's a showman. He understood human nature.

In case you lost track of what I'd written earlier. I didn't.

And you can't deny that blowback systems do work, often at pressures higher than that of the .30-30. Yes, I can. This is why the successful systems are called "hesitation blowback" and "delayed blowback" and "roller delayed" and such......
Either the case slides back or it stretches, one or the other. It doesn't just sit there absorbing the entire force of the charge without effect on the brass. YES, it does. C'MON man, this is easy to test, just do it!

The fact that oiled cartridges are used along with dry chambers and cartridges to establish the difference in back thrust on the boltface and that every published source on these shows that a dry chamber reduces back thrust by 1/3 to 1/2 but never eliminates it goes counter to the claim that chamber pressure acting on the walls can lock a case imovably without the case stretching back to meet the bolt face.
Thats an established fact of a century or more of testing cartridge pressures for the British Military and sporting rifles. This is exactly the sort of ancient "fact" that people like Ackley and Vaughn test for.

The spring back effect of locking lugs and its effect on the cartridge case was established a century ago as well. I can't see that there has been any modern improvement that would eliminate that.
Appearances can be deceiving. While appearances may be deceiving, inquiring minds will know.

PS

We apparently aren't thinking of the same sort of ringing on the breechface. My observations have been of dozens of military rifles usually only recently finding their way to the civilian market ,presumably never having been fired with reloaded ammunition, only military ammunition designed for single use, and in most cases with staked primers.
The ringing is very light and even with no sign of a cutting action or jet of gas from an imperfection of a single primer or pocket.
The appearance is that of a cummulative action of very slight leakage at the lower pressure levels rather than at peak pressure. The marking of the breechface is the result of a very slight leakage of many thousands of rounds fired, probably tens of thousands by the look of those rifles with the most noticable rings.
The appearance is usually attributed to corrosive primer gases being forced into the metal.

So unless you build a rifle using the same steels used in the early 20th century and then fire 30,000-50,000 rounds of corrosive primed military ammo through it you aren't going to be able to duplicate the sort of ring I'm speaking of.
Checking the progress of the ring's appearance every few years as you go of course.
I've noticed the same sort of rings on the breech faces of 19th century breech loaders as well, they'd also have used corrosive primers, no sign of gas cutting there either, just the surface marring and corrosion pitting of cummulative leakage at the lower ends of the pressure curve. OK, I'll agree, this isn't gas cutting.

Some things we can observe can't be easily repeatable as an experiment, life is too short.

See, the thing is...... a cartridge WILL contain the blast all by itself up to 40-55,000psi depending on brand and work hardness. That's the POINT of Ackley's experiment. And you can test it too. Easily. But unless you do, please don't just flip out unsupported theory. Some of us DO this stuff.

al

 

[Old Gunner]

See, the thing is...... a cartridge WILL contain the blast all by itself up to 40-55,000psi depending on brand and work hardness. That's the POINT of Ackley's experiment. And you can test it too. Easily. But unless you do, please don't just flip out unsupported theory. Some of us DO this stuff.

al

So you've fired a full charged high powered rifle cartridge without any form of breechblock without it blowing out of the chamber? Cause thats basically what Ackley's experiment suggested.
If the cartridge case locked to the chamber walls by chamber pressure alone could withstand the entire force of the charge then an electrically primed cartridge with no primer pocket could simply be placed in a bore open at each end and fired successfully, the only system similar would be the recoil less rifle that vents more than half its gas through a venturi and uses a deliberately vented casing.
The toughest Military .30-06 case can hold up to .06 headspace for a single firing, and thats not a certainty. That sort of military case still stretches mightly and does not just sit there with the primer supporting the casehead away from the breechface.

From my observation of the effects on brass of the .303 under various conditions of headspace loadings from the 38,000 to 46,000 psi levels and quality of brass from a half dozen sources , including Winchester manufactured Brass, the result is always that the case will either slide back slightly or stretch, and never be held back from the breechface.

The .303 case is a tapered rimmed bottle neck cased cartridge similar to the .30-30 and the main difference being size. It has much more surface area to grip the chamber walls so if grip on a dry chamber could lock the case immovably the .303 would be more certain to be locked in place than the .30-30.
One of my .303 rifles had generous headspace even for military specs and a fairly rough chamber. It held the case as close to immovable as you'd get, and in every firing the case stretched, no charge that generated pressure high enough to grip the chamber walls did not also stretch the case.
The same rifle with new bolt and bolt head now has good headspace, tighter than the minimum military specs and fired cases do not show any annular ring stretching even under highest pressure loadings with fresh brass or brass reloaded many times. Cases fired with highest pressure loads of 46,000-48,000 still chamber without undue effort and loads even a hair lighter look like unfired cases and chamber easily with only neck sizing.

Another rifle has headspace on the tight side for the military specs, though looser than optimal for a commercial rifle. This particular rifle has the best cut barrel and chamber I've seen and may be a BSA target grade barrel, Still looking for confirmation on that. It has the only Military barrel of its type that has Nominal .303-.311 dimensions rather than the looser bore of the standard Enfield barrel. The chamber is tight and mirror smooth though the rifle is over 90 years old. This rifle has never stretched the case of either Winchester factory ammo or any reloads tried in it. The cases slide back to allow the base to contact the breechface, every time. Chamber finish is the deciding factor in how these two rifles handle cases under pressure.

Either the case slides back or it stretches, one or the other. It doesn't just sit there absorbing the entire force of the charge without effect on the brass.

YES, it does. C'MON man, this is easy to test, just do it!

I've fired many thousands of rounds of many different chamberings and a wide variety of action types. The brass is always effected, it will either stretch or slide back. If it doesn't stretch past its elastic limitation it will snap back to very near original size and shape, those are facts.
If a case has no support from a breech face it will be blow out the breech, either in one piece or in several with a separated section left in the chamber.
The only thing that could prevent that would be a flash hole large enough that the vast majority of the gas blew out the primer pocket like a rocket exhaust.

The spring back of the locking lugs and surfaces is a known factor, Without it no high pressure cartridge could be easily extracted. The Winchester Lever actions were well known to have a goodly amount of spring back, necessary since they had poor primary extraction.

All calculations on the amount of force a primer cup can apply to the breech face compared to the recorded back thrust of a cartridge fired dry in a dry chamber compared to an oiled cartridge suggest that the primer alone can't overcome back thrust even when the case must stretch to reach the breechface. And that the dry case can not absorb the full thrust without stretching back to meet the breech face, otherwise there would be no pressure readings for the dry case firings.

The primer pocket expands at double the rate of the outside diameter of the case head, and the case head is the toughest brass of the entire case so it has the greatest level of elastic recovery.

Propellant charges have a pressure curve, the forces on the inside of the case are not constant throughout the burning time and bore travel, and the primer pocket is pressurized by the propellant charge to a much greater level than the primer charge can produce. This is most obvious when primers are flattened by an overload. Primers fired without a charge show very little signs of pressure at work on the cup.
The flash hole acts to meter the entry and later release of propellant gases into the pocket and cup.
Its easier to puch an expended primer out than it is to seat it, or to seat a fresh primer when reloading that case, if no spring back of the primer pocket took place the opposite would be the case and expanded primer cups would be extremely difficult to remove.
Low pressure leakage resulting in corrion of breech faces of older rifles is another known phenomena. At higher pressures the cup seals completely otherwise there would be gas cutting of the breech face at every shot.

The only way to observe these actions as they take place would be an ultra high speed camera and flouroscope capable of taking a clear image through receiver and barrel shank.
It can't be observed by the naked eye.
The only way to determine the order of events is to observe the effects of those events and then extrapolate from known facts.

PS
Comparing the .303 to the .30-30 is not Apples and Oranges, Its more like comparing a valencia orange to a tangerine.

Also if you still belive that chamber pressure working on case walls alone can lock a case immovably in the chamber there are some pretty graphic images available showing what happens if a shooter unlocks the bolt after a hang fire and the cartridge then ignites.

Also I checked Hatcher's Notebook on the testing of the .30/06 with headspace .06 over minimum. One thing they found was that when headspace is excessive it can allow a great deal of blowby as the bullet first exits the case mouth.
Ackley's Winchester would have been venting gase around the bullet. What effect that had would take some figuring.

 

[Boyd Allen]

A couple of observations about these sort of discussions...

It is easy to get caught in a PSI trap. That is to say a low strength material can support a high load if the supporting section is large enough. Also the ratio of the cross sectional area of the brass at a particular point and the area of the case being acted on that is perpendicular to the case wall should be considered. Loads should be looked at in pounds which are the result of PSI times the area the pressure is applied to, and it is that load which is the axial load that a case sees, until it stretches to the point that it is supported by the chamber and bolt face. This is why a magnum has more bolt thrust than a .222 when they are loaded to the same pressure.

Also, with many factory loads, that start out with generous "headspace" and which are not loaded to the upper limit of pressure, the primer protrudes slightly on a fired case, about .002. this can be most easily observed by holding the case lengthwise between the jaws of a dial caliper, and putting a light source behind the on the opposite side from the observer's eye. With higher pressure ammo, like some of the factory Swift loads, this is not the case. Primers are flush, not counting any cratering that may be present.

 

[Old Gunner]

A couple of observations about these sort of discussions...

It is easy to get caught in a PSI trap. That is to say a low strength material can support a high load if the supporting section is large enough. Also the ratio of the cross sectional area of the brass at a particular point and the area of the case being acted on that is perpendicular to the case wall should be considered. Loads should be looked at in pounds which are the result of PSI times the area the pressure is applied to, and it is that load which is the axial load that a case sees, until it stretches to the point that it is supported by the chamber and bolt face. This is why a magnum has more bolt thrust than a .222 when they are loaded to the same pressure.

Then would the much greater surface area of the .303 case body not give far more grip at the chamber walls than a .30-30 case at the same pressure levels?

Also, with many factory loads, that start out with generous "headspace" and which are not loaded to the upper limit of pressure, the primer protrudes slightly on a fired case, about .002. this can be most easily observed by holding the case lengthwise between the jaws of a dial caliper, and putting a light source behind the on the opposite side from the observer's eye. With higher pressure ammo, like some of the factory Swift loads, this is not the case. Primers are flush, not counting any cratering that may be present.

No dispute that primers can be seen to protude, I'm saying that its not because the primer can somehow hold the casehead away from the breechface under a full charge, not to mention upper limit charges.
The area the gases of the primer produces can push against is tiny compared to the area the gases the charge pushes against, and much if not most of the pressure inside the primer cup as it is held against the breech face comes from the powder charge rather than the tiny amount of primer compound in the cup. The vast majority of the available gases produced by the primer compound is sent directly into the case at the moment of ignition, after that propellant gases are vented back into the primer pocket as the powder charge reaches the height of the pressure curve.

.30-30 cases I've examined more often than not show protusion to the limit of head clearance, and the primers show full pressure engraving of machine marks of the breech face. The base also shows that full contact with the breechface was made, the appearance of the headstamps shows none of the fresh look of an unfired base.
So the protusion must have come after the full force of the charge was expended, but while some force was still at work on the primer and the case was rebounding into the chamber, by locking surface spring back, probably assited by residual pressure in the primer pocket, as the case snapped back to near original dimensions from temporary elastic deformation.

The harder the base of the cartridge is pressed into the breechface the more spring back there is.

One case I have handy shows not only full contact of the primer under full pressure but significant cratering from higher than average pressure, yet it protudes just as you'd expect from a low pressure load. Headstamp lettering shows the appearace of full and even contact under pressure.

A set of figures for oiled vs dry chamber pressure testing of the .30-30 done by a British proof house with base crusher pressure gun would be useful.


PS
I looked into how the plasti gauge is recommended to be used to obtain a chamber pressure figure.
Its not the same material I'd read of and seen advertised years ago, and is not used in the same manner. I can remember another similar material used to obtain pressure but not the details at the moment.

 

[Boyd Allen]

"'The harder the base of the cartridge is pressed into the breechface the more spring back there is."

Um...then why is it that my highest pressure loads are flush, and only the medium pressure show the protrusion that I wrote about in an earlier post? As to the difference in cling between the .303 and the 30-30, frankly, I don't have any data. That is the problem with these sort of discussions, lack of hard data.

 

[Old Gunner]

"'The harder the base of the cartridge is pressed into the breechface the more spring back there is."

Um...then why is it that my highest pressure loads are flush, and only the medium pressure show the protrusion that I wrote about in an earlier post? As to the difference in cling between the .303 and the 30-30, frankly, I don't have any data. That is the problem with these sort of discussions, lack of hard data.

Perhaps because your highest pressure loads put enough stress on the brass that the spring back of the locking surfaces doesn't entirely overcome the level of plastic deformation.
I figure its mostly a matter of timing, of the amount of force exerci
sed on each element during the various points of the pressure curve.
Visible effects vary according to the type and burning rate of the propellant.
Springback is only one element of what goes on in the chamber, not a answer to very part of the question.

If the data were easily available I wouldn't have presented my theory and asked for imput.

There should be a balance point and a tipping point for each individual situation of pressure level , quality of brass, chamber finish, etc.

I don't doubt that the initial force of the primer detonation can drive the case forwards, some case designs more than others, and quality of the alloy of the case is an important factor.

I did a little looking about and did find that Federal .30-30 ammo has in the past reacted differently than more common brands, and that there was a recall of Federal primers at about the time I found most of the .30-30 cases I spoke of. So thats a wild card.

If I'm correct in my main point theres a moment in time when the pressure level in the case body has dropped while theres still a tiny amount of pressurized gase in the pocket, and the brass of the case head is still slightly radially expanded, well within its elastic limitation.
The amount of chamber pressure acting on the primer cup could be enough in a higher pressure loading that it overcomes the elastic limit of the cup, while at a lower level the cup can contract faster than the case head can recover.
The difference would be miniscule, but would leave the cup momentarily free to push back against the breechface as the case is bounced away from the breechface by lug spring back and at the same time the case body is recovering from elastic deformation.

The hard data on the .303 cases reaction to firing in a dry chamber with dry case, compared to an oiled case goes counter to Ackley's stated results with the .30-30.
Every source I've found states that the dry chamber and case only relieves from 1/3 to less than 1/2 of the back thrust on the breechface, which goes against the Ackley claim.
In my own limited experiance and observation every thing I've seen suggests that the case body will do one of two things under pressure, it will either slide back to meet the breech or stretch back to meet the breech. It will either stretch beyond its elastic limits or it won't.

The Evans blowback action using the tapered case .30 carbine in a chamber deliberately indented to provide a mechanical lock between case body and chamber wall could only slighty slow down rearward movement of the case, and that at very near the chamber pressure of the .30-30. The Evans was a handgun with a fairly short barrel for that chambering otherwise the bullet would not have left the barrel before the case could be ruptured on opening by remaining pressures.

I recently ran across someone who was planning to test Ackley's claim by firing a .303 with dry chamber in an Enfield with bolthead removed, so the subject took on a bit more importance than otherwise.
There seem to be an increasing number of young shoters that grew up watching Jackass TV and will try just about anything with little regard to safety.

The main attraction of the rimmed cartridges as far as I'm concerned is that regardless of how light a load is the case isn't going to shorten past its original dimensions. Whether the primer protudes or not isn't of much importance so long as headspace was within safe limits to begin with.

The .30-30 is of some interest to me because I'd considered having a barrel turned in that chambering for an Enfield action I have that won't take a standard replacement barrel. The .32 Special is a better choice for my purposes with this project, but finding a reasonably priced barrel or blank with the slow twist is not going to be as easy.

And as I've said before when a phenomena can not be observed directly in real time the only way of figuring it out is by observing visible effects and extrapolating from known facts.
Some known facts are easy to overlook if the appearances fit with preconcieved notions.

I'm looking at a number of clues to what may take place in order to try to establish an order of events. Clues as simple as how expended primers take less effort to remove than the effort of seating a fresh primer when reloading the same case. This suggests that the geometry of of the pocket changed momentarily while the geometry of the primer cup changed permanently, by amounts too small to be measured with available tools.
A clue that supports this is the pattern of corrosion due to primer gases contacting the breechface of rifles fired with corrosive primers for decades of hard use, which suggests a near imperceptable amount of leakage at the lower pressure levels at each end of the curve. More than likely at the very end of the curve when pressure inside the case body has dropped since at the beginning of the curve pressures generated by the primer compound itself would serve to seal the cup in the pocket preventing leakage and any leakage on the upwards climb of the curve would cause direct gas cutting rather than infiltration of gases that had to be repeated over tens of thousands of rounds and many years to acheive the visible effect.

I've spent far more time examining antique rifles than modern rifles, the older guns can show effects that modern rifles won't show within our lifetime.
Not an absolute since we can find rifles a century old that have fired fewer rounds in their carreer than a Walmart bargain bought last year.
I've examined Boer War Mausers on the edge of being completely worn out and other rifles of the same period that showed no visible signs of having ever been fired. In general those rifles that show signs of hard use will have a ring on the bolt face unless the bolt or bolthead has been replaced at some point.

 

[John Kielly]

I'm looking at a number of clues to what may take place in order to try to establish an order of events. Clues as simple as how expended primers take less effort to remove than the effort of seating a fresh primer when reloading the same case.

How about the probability that depriming domes the primer cup slightly, relieving pressure/tension/call it what you will at the cup wall while seating possibly/potentially/actually in some cases flattens the crown of the cup, thus slightly expanding the flange beyond nominal diameter. I'm reasonably sure that is the reason for my last batch of PMC Russian LR primers being so finicky to seat, as they have a substantially larger radius that earlier ones I bought, somewhat like some you see in surplus European military ammo, & are thus more susceptible to expanding in diameter as pressure is exerted on them.

 

[Old Gunner]

How about the probability that depriming domes the primer cup slightly, relieving pressure/tension/call it what you will at the cup wall while seating possibly/potentially/actually in some cases flattens the crown of the cup, thus slightly expanding the flange beyond nominal diameter. I'm reasonably sure that is the reason for my last batch of PMC Russian LR primers being so finicky to seat, as they have a substantially larger radius that earlier ones I bought, somewhat like some you see in surplus European military ammo, & are thus more susceptible to expanding in diameter as pressure is exerted on them.

Could be factors to look into.
I haven't seen any doming of the face of the primer cup in any expended primers I've removed, and I sort of doubt that pressure on the center of the face transfered by the anvil would distort the walls of the primer cup. any distortion should go no further than the edges of the cup face, certainly not down the full length of its wall.
A tightly fitting primer cup would swage down to fit the pocket, with some spring tension depending on the metal used to make the cup, more so than a cup that was closer to specs for that case type. The amount of expansion when fired should depend on the elasticity of the metal rather than the preload of tension against the pocket wall.

I've used standard US manufactured primers in early production Seller&Bellot .303 that had very tight cups and a radius at the bottom that often caused detonation while seating until the pockets were reamed a polished.
Those that did seat sucessfully without reaming the pocket took quite a bit of force to seat, but when the expended primer was punched out it took no more force than it would from a US Manufactured case.

Seating a fresh primer normally causes some flattening of the cup face and a slight compression of the mixture between cup and anvil. This has been said to be necessary for consistent ignition.
I have cartridges in my collection that have perfectly curved domed primer cups, and must have been seated at the factory using a tool with an indentation shaped to perfectly fit the domed cup. The edges of this sort of primer cup are set a hair below the edges of the pocket while the apex of the dome is pretty much even with the rim or slightly below that.

 

[Old Gunner]

OG, domed primers were seated with a tool made for that and for many years, both flat and domed primers and tools were sold. I believe that Winchester and Western were the makers of domed primers, the last ones I've seen installed were the 8 1/2G primers in the WCC 58 match ammo. Those primers were mercuric and corrosive - the last US commercial use of such a primer - but Western believed their accuracy was superior to any other. By 1960 they had changed to a non-mercuric, non-corrosive primer (8 1/2-120) which was a very good primer and harmed neither brass nor steel.

Just dug out another cartridge with Domed Primer, a .45 ACP it appears to be a WC headstamp. I'll scan it later. I don't doubt that these were a signature Winchester type, though its possible other less well known makers used it as well at some point.

I took a look at Hatcher's Notebook to see what he had said about barrel time, he gave the figure of .00098 second for the .30/06 ball of his day, aproximately one millisecond is a reasonable estimate for .30 cartridges with variation in ultimate muzzle velocity and barrel length making it fall to one side or the other, so whatever takes place in the chamber during the pressure curve would be measured in micro seconds, too fast to really get a good grasp of and probably too fast for any visual recording instrument available even if it could give a clear image through the steel of receiver and barrel shank.

this from VarmintAl's site

Increasing the Coefficient of Friction to 0.55 the brass case head never does contact the bolt face for the
35,000 peak chamber pressure load. This condition would have the primer protruding slightly.

His calculation of COF= 0.55 represents a chamber rough as a cobb, not commonly encountered in any high quality rifle unless its been heavily corroded or poorly rechambered.
35,000 PSI is far below the max pressure encountered with the .30-30 at 42,000 PSI and the ,30-30 case is much smaller in diameter than the .243 Al used as a basis for his calculations.

In Al's calculations the timing is everything, and he leaves out a number of factors that I've tried to determine the effects of.

I'll leave this for now, too many numbers running wild in my main frame, I'm begining to feel like Bender after he first saw the numeral 2.