The above quote is from an older thread in response to someone having over pressure catastrophe; stuck bolt, blown primer, weldee/fused case and bolt. Ive seen this response on several threads in past. Now I know that many gunsmiths back in the "old days" used lubed cases on a standard load, mostly military standard loads as "proof loads". So if the bolt lugs didnt shear or the action crack or stretch then it was OK to go out the door. This acton could certainly put all or most of the case head thrust on the bolt face, but nothing more. So why do posters keep quoting this saw when someone has mysterious case failure or brimer blow out, etc,etc. a. n.?
lubed chamber, huh?
- Thread starter rogn
- Start date
Dusty Stevens
Shiner
Only time ive seen it mentioned is when theres an overpressure situation and upon further investigation the OP lubed the brass or chamber. Itll make a normal load seem severely hotter
This topic is somewhat covered in the Rifle Accuracy Facts book. I can't recall perfectly but it seems like there was only 1800lbs of bolt face thrust in a meticulously clean case and chamber and somewhere around 6500-7000lbs with a lubed case. Don't hold me to these numbers but I think they are pretty close.
This is also why Im not a fan of mirrored chambers.
Below in Britain a different crusher pressure method was developed and it is still used in a few proof houses today.
Cartridge Pressure Standards
http://kwk.us/pressures.html
In Britain, a third set of crusher standards were developed, using a "base" crusher. The crusher was a short, thick tube placed behind a piston at the base of the cartridge, and the firing pin passed through the center. The cartridge case was well oiled before firing, to minimize cling to the chamber walls (if not oiled, the indicated pressures were about 25% lower). To prevent case rupture on set back of the base, the crusher was first deformed in a press to a pressure a bit lower than that expected in firing. The units were generally stated in British long tons per square inch, or tsi. Pressures indicated by this method run 10 to 20% below those indicated by radial crushers. Kynamco in England still rates their production cartridges with this method.
Below from the 1929 British Textbook of Small Arms and proof testing the Enfield rifle. Two oiled proof cartridges were fired during proof testing and if the headspace increased .003 or more the rifle failed proof testing. To this day the British military still uses this proof testing method of two oiled proof cartridges. In the U.S. only one "dry" proof cartridge is used for proof testing to SAAMI standards.
Below the British Enfield rifle had changeable bolt heads used to adjust the rifles headspace. Just don't tell anyone I played with my bolt head till I nearly went blind.
NOTE, if the Enfield rifle was at the max headspace of .074 and a case with a rim thickness of .058 you would have .016 head clearance. And with most rifles today you only want .001 to .002 shoulder bump that equates to the same approximate head clearance.
There is a math formula for computing bolt thrust, "BUT" it is not accurate. Many of you have made workup loads and the primers are protruding from the base of the case at the lower loads. This means the chamber pressure was not great enough to push the case against the bolt face. You also have the dwell time the base of the case is in contact with the bolt face. This varies with the amount of head clearance, chamber pressure and the brass spring back. Believe it or not a "DRY" cartridge case acts like a cars shock absorber and reduces the amount of bolt thrust and dwell time.
Some of you may have read about P.O. Ackley's experiment with a Winchester 94 30-30 rifle. He removed the locking bolt and remotely fired the rifle and nothing happened to the rifle. The case gripped the chamber walls and at 42,000 psi the pressure was not great enough to make the rear of the case contact the bolt face. But if you use the math formula for bolt thrust it will show thousands of pounds of thrust.
Bottom line in most rifles the SAAMI chamber and cartridge drawings will show Min and Max headspace with .010 in between the two. And the more bolt thrust you have the faster the headspace will increase in time on your rifle.
Below from the H.P. White Testing Laboratory.
"1.4 Failure of a gun assembly from internal pressure may be from either
of two (2) failure mechanisms.
1.4.1 The general perception is that those failures are the result
of a single exposure to a CATASTROPHIC PRESSURE level. This
may be an over simplification in that the strength of the
assembly may have been degraded by previous repeated exposures
to excessive, but lesser, levels of pressure whose cumulative
effect is to reduce the ultimate strength of the assembly.
1.4.2 Repeated exposure to pressures which exceed the elastic limit
of a material will continually reduce the ultimate strength of
the material until the ultimate strength is exceeded by a
relatively low pressure level causing fatigue failure."
What is scary is you can buy all the parts to build a AR15 rifle and it is never proof tested.
Cartridge Pressure Standards
http://kwk.us/pressures.html
In Britain, a third set of crusher standards were developed, using a "base" crusher. The crusher was a short, thick tube placed behind a piston at the base of the cartridge, and the firing pin passed through the center. The cartridge case was well oiled before firing, to minimize cling to the chamber walls (if not oiled, the indicated pressures were about 25% lower). To prevent case rupture on set back of the base, the crusher was first deformed in a press to a pressure a bit lower than that expected in firing. The units were generally stated in British long tons per square inch, or tsi. Pressures indicated by this method run 10 to 20% below those indicated by radial crushers. Kynamco in England still rates their production cartridges with this method.
Below from the 1929 British Textbook of Small Arms and proof testing the Enfield rifle. Two oiled proof cartridges were fired during proof testing and if the headspace increased .003 or more the rifle failed proof testing. To this day the British military still uses this proof testing method of two oiled proof cartridges. In the U.S. only one "dry" proof cartridge is used for proof testing to SAAMI standards.
Below the British Enfield rifle had changeable bolt heads used to adjust the rifles headspace. Just don't tell anyone I played with my bolt head till I nearly went blind.
NOTE, if the Enfield rifle was at the max headspace of .074 and a case with a rim thickness of .058 you would have .016 head clearance. And with most rifles today you only want .001 to .002 shoulder bump that equates to the same approximate head clearance.
There is a math formula for computing bolt thrust, "BUT" it is not accurate. Many of you have made workup loads and the primers are protruding from the base of the case at the lower loads. This means the chamber pressure was not great enough to push the case against the bolt face. You also have the dwell time the base of the case is in contact with the bolt face. This varies with the amount of head clearance, chamber pressure and the brass spring back. Believe it or not a "DRY" cartridge case acts like a cars shock absorber and reduces the amount of bolt thrust and dwell time.
Some of you may have read about P.O. Ackley's experiment with a Winchester 94 30-30 rifle. He removed the locking bolt and remotely fired the rifle and nothing happened to the rifle. The case gripped the chamber walls and at 42,000 psi the pressure was not great enough to make the rear of the case contact the bolt face. But if you use the math formula for bolt thrust it will show thousands of pounds of thrust.
Bottom line in most rifles the SAAMI chamber and cartridge drawings will show Min and Max headspace with .010 in between the two. And the more bolt thrust you have the faster the headspace will increase in time on your rifle.
Below from the H.P. White Testing Laboratory.
"1.4 Failure of a gun assembly from internal pressure may be from either
of two (2) failure mechanisms.
1.4.1 The general perception is that those failures are the result
of a single exposure to a CATASTROPHIC PRESSURE level. This
may be an over simplification in that the strength of the
assembly may have been degraded by previous repeated exposures
to excessive, but lesser, levels of pressure whose cumulative
effect is to reduce the ultimate strength of the assembly.
1.4.2 Repeated exposure to pressures which exceed the elastic limit
of a material will continually reduce the ultimate strength of
the material until the ultimate strength is exceeded by a
relatively low pressure level causing fatigue failure."
What is scary is you can buy all the parts to build a AR15 rifle and it is never proof tested.
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Harold Vaughn used strain gauges to derive his bolt thrust numbers. They are surprisingly different than the British experiments. The most interesting contrast to me is that even if the quantification was different, the relativity of the data would still not match.
~from Harold R. Vaughn / Precision Shooting Inc.
Now I'm back to just guessing.
~from Harold R. Vaughn / Precision Shooting Inc.
Now I'm back to just guessing.
Harold Vaughn used strain gauges to derive his bolt thrust numbers. They are surprisingly different than the British experiments. The most interesting contrast to me is that even if the quantification was different, the relativity of the data would still not match.
Now I'm back to just guessing.
I'm confused, what are you referring too in your statement above?
Because a lot of people still think it's OK to lubricate your cases or the chamber, most do it because they think it's some kind of magic that extends the life of their cases.
And as was mentioned, while a proof load shouldn't damage a rifle, that pressure level is only used once. Nobody recommends using proof load pressures more than once because of the fact that stress accumulates in steel and while the life of the rifle wont be reduced drastically using one proof load, the usable life will be reduced exponentially with every subsequent proof load.
Sorry, I don't even understand what I wrote. Lol
I was referring the the huge discrepancy between the numbers from the British crush test and Vaughn's strain gauge test.
In one of the articles posted here by Laurie Holland he posted the photo below of fired factory loaded Remington 7mm Mauser cases. He stated that the old mauser rifle had excessive headspace. "BUT" to me it also shows that the chamber pressure was not great enough to push the case back against the bolt face.
Below on the right shows how the primer will back out on reduced cast bullet loads on a old Enfield rifle
Below is a animated image of a .303 British cartridge at normal chamber pressure being fired at the max headspace of .074. The primer protrudes but then the higher chamber pressure causes the case to be pushed into the bolt face, and the case stretches and thins.
In Enfield forums I was always in running gun battles with the "briliant" reloaders who told people it was OK to lube their cases to prevent the case from stretching and thinning. They just didn't understand that the older No.1 Enfield rifles were made from softer grade steel than modern rifles.
The last sentence in the image below from the "1929 Textbook of Small Arms" tells the whole story.
Below on the right shows how the primer will back out on reduced cast bullet loads on a old Enfield rifle
Below is a animated image of a .303 British cartridge at normal chamber pressure being fired at the max headspace of .074. The primer protrudes but then the higher chamber pressure causes the case to be pushed into the bolt face, and the case stretches and thins.
In Enfield forums I was always in running gun battles with the "briliant" reloaders who told people it was OK to lube their cases to prevent the case from stretching and thinning. They just didn't understand that the older No.1 Enfield rifles were made from softer grade steel than modern rifles.
The last sentence in the image below from the "1929 Textbook of Small Arms" tells the whole story.
The British base crusher method measured actual pressure on the bolt face, "BUT" the pressure figures are in British long tons and need to be converted to PSI. And Vaughn's strain gauge is not mounted directly on the bolt face and is not measuring pressure using the same method.
Bottom line, a dry case with shoulder bump and head clearance will produce less bolt thrust than a oiled case will.
Below the case has to stretch to contact the bolt face and this absorbs some of the load-force on the bolt face. (Like a cars shock absorber)
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Ed, my pic of the 7X57 cases you show with backed-out primers came alongside another matching one of of some cases from European RWS factory hunting ammunition, also fired in the same excessive headspace rifle. The cases from the low-pressure US ammo (actually PMC if you remember this long gone outfit) were presumed - as you've said - to have obturated correctly in the front of the chamber holding the case-head away from the bolt-face, but pressures were too low (fortunately) to stretch the case-body ahead of the web. The cases were undamaged and reloadable.
The RWS ammunition, presumably loaded to full CIP pressures or close to it, maybe thinner in the body walls too, had stretched and were scrap. Primers were very flat as if there had been over-pressure and there was a distinct thinned ring ahead of the web shown by an easily seen colour change. (There wouldn't have been over-pressure, more likely primers initially backed out shortly after ignition then were slammed against the bolt as the case stretched reseating them in the pockets but flattening them out in doing so.) These cases went into the bin, undoubtedly weakened by the experience.
When I started shooting centrefires, initially all surplus service rifles, and with mandatory proof before putting them on sale in the UK, the Enfields were all marked as proofed in 'tons', the oiled case method used as you describe. IIRC, my first 7.62mm rifle - a rebarreled Enfield No.4 - was marked as '18 tons pressure'. What I can't remember now at this remove was whether foreign imports were also so proofed back then. I think they were, but memory may be playing tricks here. The two UK commercial proof houses now test custom builds, rebarrelling jobs, new rifles imported from outside of the EU area etc using a modern electronic method as per other EU CIP equivalents.
Oiled cases or chambers in normal use? Can't believe anybody is so ignorant as to recommend this practice!
The RWS ammunition, presumably loaded to full CIP pressures or close to it, maybe thinner in the body walls too, had stretched and were scrap. Primers were very flat as if there had been over-pressure and there was a distinct thinned ring ahead of the web shown by an easily seen colour change. (There wouldn't have been over-pressure, more likely primers initially backed out shortly after ignition then were slammed against the bolt as the case stretched reseating them in the pockets but flattening them out in doing so.) These cases went into the bin, undoubtedly weakened by the experience.
When I started shooting centrefires, initially all surplus service rifles, and with mandatory proof before putting them on sale in the UK, the Enfields were all marked as proofed in 'tons', the oiled case method used as you describe. IIRC, my first 7.62mm rifle - a rebarreled Enfield No.4 - was marked as '18 tons pressure'. What I can't remember now at this remove was whether foreign imports were also so proofed back then. I think they were, but memory may be playing tricks here. The two UK commercial proof houses now test custom builds, rebarrelling jobs, new rifles imported from outside of the EU area etc using a modern electronic method as per other EU CIP equivalents.
Oiled cases or chambers in normal use? Can't believe anybody is so ignorant as to recommend this practice!
Ned Ludd
Silver $$ Contributor
Agreed...it makes about as much sense as oiling up the outside of a round of ammunition prior to chambering/firing it.
I used to argue with a guy on another forum about his habit of lubricating his cartridges for use in his Springfield M1A. He always bragged about how he could get something like twenty-something reloads on a case. He'd argue with people that told him it wasn't a good idea by referencing the design of old machine guns that were designed to use lubricant in the chamber, Col. Hatcher's Notebook, and all sorts of other "proof". I finally gave up trying to prove that it wasn't a smart thing to do.
I've got an archived copy of an article that was written in 1916 in which the author talks about why it's not good to lubricate cartridges. 103 years later and people still argue that it's a good thing. Most people will get an idea in their head and, regardless of proof to the contrary, always swear that it's a fact.
I've got an archived copy of an article that was written in 1916 in which the author talks about why it's not good to lubricate cartridges. 103 years later and people still argue that it's a good thing. Most people will get an idea in their head and, regardless of proof to the contrary, always swear that it's a fact.
BoydAllen
Gold $$ Contributor
First of all, I do not lube cases, and I am careful about leaving any lube on sized brass. Having said that, there are two situations where I would not worry much about light lubrication.
In the case where one is fire forming .220 Russian brass into 6mm PPC when using the usual PPC powders and bullet weights, the pressure and resultant velocity are much less than are commonly found in regular 6PPC loads. A film of light oil, applied only to the body of the case will materially reduce its cling to the chamber so that as pressure builds the formation of the case will result in less stretching at the back, and a more uniform head clearance. THIS DOES NOT APPLY AT ALL TO DISSIMILAR SITUATIONS. I believe that there is a difference of volume between the pre and post fireformed cases of about 15%, in this specific situation.
The other situation would be when low pressure cast bullet loads are used with rimless cases. It is common knowledge that when this takes place that as the number of shots on a case mounts up, that primer protrusion will increase incrementally, which will result in the shoulder moving back on the case, and the neck becoming longer, without the case being longer. I have not done an experiment with oiled cases with these type of loads, but if I had a suitable rifle and components, I would not be afraid to, given the low pressures involved. If the protrusion issue was improved, it might be worthwhile. I used to shoot cast, casting my own bullets for an old Springfield, and have personally experienced the primer protrusion I described.
In both of the above cases, chamber pressures are significantly below that of factory ammunition. I should add that while I have seen cases being oiled as described while fire forming PPC from Russian, with no problem, my results without the oil have given me no reason to switch.
Again, I do not oil, or recommend oiling cases or chambers.
In the case where one is fire forming .220 Russian brass into 6mm PPC when using the usual PPC powders and bullet weights, the pressure and resultant velocity are much less than are commonly found in regular 6PPC loads. A film of light oil, applied only to the body of the case will materially reduce its cling to the chamber so that as pressure builds the formation of the case will result in less stretching at the back, and a more uniform head clearance. THIS DOES NOT APPLY AT ALL TO DISSIMILAR SITUATIONS. I believe that there is a difference of volume between the pre and post fireformed cases of about 15%, in this specific situation.
The other situation would be when low pressure cast bullet loads are used with rimless cases. It is common knowledge that when this takes place that as the number of shots on a case mounts up, that primer protrusion will increase incrementally, which will result in the shoulder moving back on the case, and the neck becoming longer, without the case being longer. I have not done an experiment with oiled cases with these type of loads, but if I had a suitable rifle and components, I would not be afraid to, given the low pressures involved. If the protrusion issue was improved, it might be worthwhile. I used to shoot cast, casting my own bullets for an old Springfield, and have personally experienced the primer protrusion I described.
In both of the above cases, chamber pressures are significantly below that of factory ammunition. I should add that while I have seen cases being oiled as described while fire forming PPC from Russian, with no problem, my results without the oil have given me no reason to switch.
Again, I do not oil, or recommend oiling cases or chambers.
At 38,000 cup or 42,000 psi the primers always protrude on my 30-30 cases fired in my Winchester 94 and this is normal.
Meaning the best type cases for reduced loads are rimmed cases because the rim stops forward movement.
You can cheat with rimmed cases and slip a rubber o-ring over the cartridge to hold the case against the bolt face.
Below fire forming .303 British cases using a rubber o-ring.
Meaning the best type cases for reduced loads are rimmed cases because the rim stops forward movement.
You can cheat with rimmed cases and slip a rubber o-ring over the cartridge to hold the case against the bolt face.
Below fire forming .303 British cases using a rubber o-ring.
Dusty Stevens
Shiner
We wont be advocating oiling chambers or cases around here. This is where people come to get the correct advice. I do it in the situation boyd spoke of but thats so far out there we usually dont speak of it and it better be a top shelf custom action designed to handle the 80,000+psi we generate thousands of times a year.
Lubing cases has a history almost as old as self-loading cartridge arms; many of the early gas- and recoil-operated designs needed lubed cases to aid in early extraction while the motive force (gas or spring) was still present. It's well known in that context, but we've solved the problem in modern designs by delaying extraction (storing or timing the motive force) until chamber pressure drops. For more, I highly suggest Chinn's "The Machine Gun", firearms development history is absolutely fascinating.
Lubing in bolt guns is much simpler: it increases bolt thrust by an amount not greater than the tensile strength of the stretch ring of the case. The stretch ring is the point where the case stretches if headspace it too great, because the behavior transitions from frictional gripping of the chamber wall (because it's thin) to tensile containment of the pressure (too thick to stretch). If you observe incipient head separations in fired cases, that's where the stretch ring is; it varies up and down a bit because the transition from thin to thick varies.
The trade-off is an increase in bolt thrust, but it can never be greater than the tensile strength of the case at the stretch ring. . . because that force is the most that the case could possibly contribute with perfect friction (no lube).
I find lubing quite useful for fireforming cartridges where the marginal cost of the cases is high, and the pressure is low relative to action strength. Interrupting the friction between the case and the chamber lets the case slide back and blow the shoulders forward all the way, instead of splitting the effect halfsies between forming the shoulders and stretching the case. My .375 H&H cases are expensive, so lubing for the first few firings lets them fireform with near-zero stretching and maximal shoulder forming. Once that's done, there's really no point continuing to lube in subsequent firings.
In weapons where the case's tensile contribution is a significant portion of the action's Factor of Safety, you should not lube. It's on you to figure out what your doing, but generally I wouldn't lube: 1) a load that already hot, or 2) a load for an flexible action*. For fireforming cases free of stretch over moderate loads in strong actions, it works great.
*flexible actions are anything with suspect heat treating, and anything rear- or mid-locking (like leverguns).
Lubing in bolt guns is much simpler: it increases bolt thrust by an amount not greater than the tensile strength of the stretch ring of the case. The stretch ring is the point where the case stretches if headspace it too great, because the behavior transitions from frictional gripping of the chamber wall (because it's thin) to tensile containment of the pressure (too thick to stretch). If you observe incipient head separations in fired cases, that's where the stretch ring is; it varies up and down a bit because the transition from thin to thick varies.
The trade-off is an increase in bolt thrust, but it can never be greater than the tensile strength of the case at the stretch ring. . . because that force is the most that the case could possibly contribute with perfect friction (no lube).
I find lubing quite useful for fireforming cartridges where the marginal cost of the cases is high, and the pressure is low relative to action strength. Interrupting the friction between the case and the chamber lets the case slide back and blow the shoulders forward all the way, instead of splitting the effect halfsies between forming the shoulders and stretching the case. My .375 H&H cases are expensive, so lubing for the first few firings lets them fireform with near-zero stretching and maximal shoulder forming. Once that's done, there's really no point continuing to lube in subsequent firings.
In weapons where the case's tensile contribution is a significant portion of the action's Factor of Safety, you should not lube. It's on you to figure out what your doing, but generally I wouldn't lube: 1) a load that already hot, or 2) a load for an flexible action*. For fireforming cases free of stretch over moderate loads in strong actions, it works great.
*flexible actions are anything with suspect heat treating, and anything rear- or mid-locking (like leverguns).
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