i know how important it is to load using the proper amount and burn speed is. im not looking to test more power untill my barrel blows up but i am wondering if there is a way to find out how much pressure a barrel is rated for?
how do you know what max pressure of a barrel is?
- Thread starter AKD
- Start date
The barrel is the typically the toughest part of the pressure holding portions of your firearm.
The weakest link is the case, usually followed by the action.
As stated above, stick with published loads proven to provide multiple loadings in your casings.
There is this funny thing called Cumulative Metal Fatigue which makes any sort of predictability to how long over pressure loads can be handled by a firearm.
Stick to the book loads
The weakest link is the case, usually followed by the action.
As stated above, stick with published loads proven to provide multiple loadings in your casings.
There is this funny thing called Cumulative Metal Fatigue which makes any sort of predictability to how long over pressure loads can be handled by a firearm.
Stick to the book loads
Yes - Go spend six years in university studying mechanical engineering. Specialize in stress analysis and fracture mechanics. Then come to the conclusion that its a very complicated subject, and best left to experts. Short of it is, barrels are designed to stress levels that are known to be safe at the expected levels of pressure. Its very difficult to predict the actual point of failure - unless you do a destructive test. Even then, one rifle may fail at a different pressure than its sister off the assembly line.
Heed the advice that others have given you...
Heed the advice that others have given you...
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While it is normally true that the case is the weakest link, there are two examples I can think of very quickly that might be viewed as exceptions. Both the .45/70 and the .303 Brit are cartridges that can exceed the safe pressure of some of the rifles chambered for those cartridges. A .45/70 Trapdoor Springfield cannot be safely loaded to the pressure that would be safe in the Ruger #1, and the .303 can be loaded to pressures making it the equal of the .308 when loaded in a P-14, but that load could not be safely fired in a Lee Metford.
Provided your rifle is a modern bolt action, a sticky bolt indicates that you have exceeded the safe pressure and should back off. If you have a chronograph (if you don't, get one, its the best hundred bucks you'll spend.) when, you are working up a load and observe that you have matched the maximum book velocity, regardless of your load, stop. Little can be gained by attempting to outdo the book, and the maximum load listed was determined to produce the highest safe pressure in a test barrel. If you observe a sticky bolt before that velocity is realized, stop and reduce your load, or switch to a more suitable powder. Actions other than bolt guns are not as strong, and should not as a rule be loaded as heavily.
The chronograph can also be used to determine the maximum load by observing a velocity plateau with uniform powder weight increments. If you started at the suggested starting load and loaded in 1 gr increments, when you see that the increase in velocity is only 10 fps instead of 40 fps, that's the plateau, and the next powder increment will probably result in a sticky bolt. I generally consider the load prior to the velocity plateau as my maximum working load. It I want to tweak the load fort accuracy I work down from that point.
With regard to burn speed, if the powder is too slow, you will not achieve the velocity, or the pressure necessary to achieve that velocity, due to the limits of your case capacity. If on the other hand your powder burn rate is too fast, you will observe excessive pressure before you achieve the velocity you desire. The loading manuals to a large extent remove the risk of using an inappropriate powder, when the aim is to produce full powered loads. If you want to make loads that are below 2000 fps with modern rifle cartridges, it is best to consult data for cast bullets to use as a guide line. The Lyman Cast Bullet Handbook is a good reference.
Have been reading again the experiments of Parker Ackley blowing up military actions.
To properly test the action, he fitted each with a large diameter, high tensile strength barrel, chambered for the 270 Ackley magnum. This would indicate that he considered the barrel would be the first to go.
Here is a quote from his summations.
"The Jap 6.5 action was the big surprise of the tests. The indications are that this action will be the strongest one that will be tested, regardless of origin or make. In fact the three actions tested could not be blown up with any load that the barrels would stand. The barrels used throughout the tests were of very much higher tensile strength than any normal factory barrel available, or any military barrel regularily used. They were also of large diameter, being at least 1-3/16" at the breach. In every case the Jap actions, after the barrels had been ruptured, or blown completely free from the action, were still serviceable and showed no apparent weakness with the one exception when the bolt plug or safety was blown out of the bolt. This was directly due to the fact that the firing pin hole in the bolt was very badly oversized------ After the firing pin hole was bushed to make a tight fit for the firing pin, no more trouble was experienced."
Another tidbit.
"The Enfield action proved somewhat of a disappointment in these tests.------However the two that have been tested so far are widely different in physical characteristics. That is, the heat treatment given the two actions varied a great deal. One acion was somewhat hard and blew up rather easily. When the blowup occurred, the action was nearly disintegrated and is one of the few blowups which would have perhaps proven fatal to the shooter."
"The other action (Enfield) was extremely soft."
To properly test the action, he fitted each with a large diameter, high tensile strength barrel, chambered for the 270 Ackley magnum. This would indicate that he considered the barrel would be the first to go.
Here is a quote from his summations.
"The Jap 6.5 action was the big surprise of the tests. The indications are that this action will be the strongest one that will be tested, regardless of origin or make. In fact the three actions tested could not be blown up with any load that the barrels would stand. The barrels used throughout the tests were of very much higher tensile strength than any normal factory barrel available, or any military barrel regularily used. They were also of large diameter, being at least 1-3/16" at the breach. In every case the Jap actions, after the barrels had been ruptured, or blown completely free from the action, were still serviceable and showed no apparent weakness with the one exception when the bolt plug or safety was blown out of the bolt. This was directly due to the fact that the firing pin hole in the bolt was very badly oversized------ After the firing pin hole was bushed to make a tight fit for the firing pin, no more trouble was experienced."
Another tidbit.
"The Enfield action proved somewhat of a disappointment in these tests.------However the two that have been tested so far are widely different in physical characteristics. That is, the heat treatment given the two actions varied a great deal. One acion was somewhat hard and blew up rather easily. When the blowup occurred, the action was nearly disintegrated and is one of the few blowups which would have perhaps proven fatal to the shooter."
"The other action (Enfield) was extremely soft."
- Location
- Calgary, AB
Yes.....the degree of heat treatment in concert with the specific steel alloy is the most important parameter in properly placing the strength of pressure vessels; then the next significant parameter is the wall thickness of the vessel (barrels in this case). Barrels must receive proper heat treatment to have a YIELD strength with a safety factor of about twice the normal working pressure that they are EXPECTED to see in service. If they are heat treated significantly beyond this level they become dangerously brittle (un-ductile) and have the potential to shatter (brittle fracture) when exposed to the impact loading during firing (pressure peak achieved in about 1 millisecond). The most common rifle barrel steel is 4100 series chromium-molybdenum steel which can range in tensile yield strength from around 60,000 psi (annealed) to 240,000 psi (oil quenched & untempered); both of these extreems are totaly unsuited for barrel service. What is usually done is a 4140 steel is oil quenched from its austinizing temperature, then tempered at about 1100 F resulting in a tensile yield strength around 120,000 psi, providing a safety factor of approx. twice the 60,000 psi range of the top end loads.
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Not to rag on Nutz but...
AKD asked a valid question, he just didn't word it right, resulting in poor though for the most part interesting answers. (boomer, H4831 and thecollector had great comments, good reads that I wouldn't have read anywhere else, but I don't think they answered AKD's question. Cosmic however didn't even try
)
Is there a book that has the MV's for diffrent length barrels so as to stay safe? IE: 2500FPS in a 16" barrel would be running significantly higher PSI than 2500FPS in a 22" barrel right?
Do aftermarket barrels have diffrent pressures than SAAMI specs, or is this all assumed as part of the Cal?
I don't know AKD, but I think we're in the same boat. I'm learning as much as I can so that when I get some money together, I don't waste it and don't hurt myself.
No kidding, but his question was for "Rated Pressure" not "Total Failure Pressure"
I know you guys were trying to help, but he's a newb and we shouldn't be punnished with patrinising comments because we didn't ask the question right or the right question: Help us ask the questions we need to be asking.
AKD has 11 posts on CGN.
AKD asked a valid question, he just didn't word it right, resulting in poor though for the most part interesting answers. (boomer, H4831 and thecollector had great comments, good reads that I wouldn't have read anywhere else, but I don't think they answered AKD's question. Cosmic however didn't even try
)Is there a book that has the MV's for diffrent length barrels so as to stay safe? IE: 2500FPS in a 16" barrel would be running significantly higher PSI than 2500FPS in a 22" barrel right?
Do aftermarket barrels have diffrent pressures than SAAMI specs, or is this all assumed as part of the Cal?
I don't know AKD, but I think we're in the same boat. I'm learning as much as I can so that when I get some money together, I don't waste it and don't hurt myself.
No kidding, but his question was for "Rated Pressure" not "Total Failure Pressure"
I know you guys were trying to help, but he's a newb and we shouldn't be punnished with patrinising comments because we didn't ask the question right or the right question: Help us ask the questions we need to be asking.
AKD has 11 posts on CGN.
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- Location
- Somewhere on the Hudson Bay Coast
There is a rule of thumb that dictates something to the effect that for cartridges with a muzzle velocity over 3000 fps there is a gain or loss of 40 fps per inch change in barrel length, 20 fps per inch at 2500 fps and 10 fps per inch below 2000. I probably don't have it exactly right but its all hogwash anyway as there are many variables that form the elements that can effect the velocity of any given bullet from any given barrel. For example, I have a .308 with a 28" barrel. According to the formula, the fastest I should be able to drive a 200 gr bullet from that barrel is 2500 fps (2400 fps from a 24" barrel + 20 fps/inch of barrel) yet I have chronographed 200 gr Matchkings at 2700 with no evidence of excess pressure. Conversely there have been a couple of fellows posting on here who report that when they cut their .375 H&H Brno 602's from 25 " to 20" they only lost 50 fps. I have seen several 4" revolvers produce equal or higher velocity than 6" revolvers of the same make and model.
The smoothness of the internal barrel surface effect velocity. The uniformity of the internal bore dimensions effect velocity. The barrel's rate of twist effects velocity. Freebore effects velocity in that barrels with excessive freebore produce lower pressure so more powder can be added to the charge resulting in the production of a greater volume of gas and higher velocity. The length of the bullet's bearing surface effects velocity. In the case of a revolver, the amount of cylinder gap effects velocity.
I hope this is a better answer to the original post.
The smoothness of the internal barrel surface effect velocity. The uniformity of the internal bore dimensions effect velocity. The barrel's rate of twist effects velocity. Freebore effects velocity in that barrels with excessive freebore produce lower pressure so more powder can be added to the charge resulting in the production of a greater volume of gas and higher velocity. The length of the bullet's bearing surface effects velocity. In the case of a revolver, the amount of cylinder gap effects velocity.
I hope this is a better answer to the original post.
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You will likely get better answers, if you clarify why exactly you want the information.
I've never seen barrels rated for pressure, except that, in the cases of black powder and rimfire cartridge barrels, they sometimes say that the barrel is not for use with high pressure cartridges. Usually, those are barrels made from 12L14, or 1137, or similar alloys, that machine freely, but do not have a high tensile strength.
Basically, I guess, the short answer is that you are pretty much wasting time looking at what the barrel may be capable of, as they don't "rate" barrels. If you need it to withstand pressure, you would build it larger, based on the material used. Think "soda straw" compared to 2 inch steel bar with same size hole as soda straw. Both have the same size bore, but one will be able to withstand a higher pressure.
The practical upper limits of pressure for a brass cartridge case have been around 60,000 psi. That pressure level does not last very long when the powder goes.
The case is usually the limiting factor, as explained above, in a previous post.
Cheers
Trev
Thanks. Is there a realy good book with these rules of thumb in them? Not sure I'd push the 2500 fps being scared of the long term "Cumulative Metal Fatigue" as Lefty put it.
That said, if you slowly bring the pressures up and don't see case damage, you feel that the gun is not being damaged either?
Again if I was to spend the next couple of weeks reading, what should I read?
That said, if you slowly bring the pressures up and don't see case damage, you feel that the gun is not being damaged either?
Again if I was to spend the next couple of weeks reading, what should I read?
Still, it depends what you have in mind;
With suitable (normalized) loads for caliber/ammunition, a modern rifle will last longer than you.
The metal used today have much better tensile strenght than the mild steel used in the turn of the 19th century 'til after WWII.
The heat treatments are also much better today (better controlled temperature / curburizing process etc).
If you want to know how the rifles are tested, SAAMI and CIP use the MAP (maximum Average Pressure) as a guide line for the strenght of a rifle. The commercial ammunition are loaded to about 85% of the MAP to provide a certain margin of security (to both themanufacturers and the users). Then, let's say for CIP, there is the static pressure test, wich is usually based on 15% increase of the MAP pressure. Then the Proof Test is done at a pressure 25% higher than the MAP pressure.
Let's take the .308 Win / 7.62X51NATO for example;
In the "Small Calibers, US Army tm43-0001-27" the US military standard for the 7.62X51 NATO is stipulating a Maximum pressure of 50 000 PSI and a Proof test of 67 500 PSI.
As for SAAMI, in their datas book (Z299.4-1992) the MAP for the .308 Win is 62 000 PSI, the mnimum proof Pressure is 83 000 PSI and the Max. Proof Pressure is 89 000 PSI.
Then CIP, in the TDCC they state (for the .308 Win again);
MAP of 4150 bar (60 175 PSI), a PK (max static pressure) of 4773 bar (69 209 PSI) and a PE (average proof test pressure) of 5190 bar (75 255 PSI). They also provide a minimum energy level for the poof test, EE of 3920 Joules.
The difference between both CIP and SAAMI datas looks big but in fact it is not, both standards using different methods of measuring (location and transducers) the pressure. Norma published their .308 Win loads as being in the 49 000 PSI.
If it's curiosity that drives you, have a look to this (hope you understand swedish, though) http://www.testfakta.se/Article.aspx?a=16439
And for more graphic stuff, look at this; http://www.testfakta.se/Article.aspx?a=16350
As you will see in there, if the pipe is clogged, it is this part (the barrel) wich will fail (Browning and Remington deplorably failed at this test), not the action.
Give us a better explaination of what you have in mind and it will be easier to bring you to the right information.
With suitable (normalized) loads for caliber/ammunition, a modern rifle will last longer than you.
The metal used today have much better tensile strenght than the mild steel used in the turn of the 19th century 'til after WWII.
The heat treatments are also much better today (better controlled temperature / curburizing process etc).
If you want to know how the rifles are tested, SAAMI and CIP use the MAP (maximum Average Pressure) as a guide line for the strenght of a rifle. The commercial ammunition are loaded to about 85% of the MAP to provide a certain margin of security (to both themanufacturers and the users). Then, let's say for CIP, there is the static pressure test, wich is usually based on 15% increase of the MAP pressure. Then the Proof Test is done at a pressure 25% higher than the MAP pressure.
Let's take the .308 Win / 7.62X51NATO for example;
In the "Small Calibers, US Army tm43-0001-27" the US military standard for the 7.62X51 NATO is stipulating a Maximum pressure of 50 000 PSI and a Proof test of 67 500 PSI.
As for SAAMI, in their datas book (Z299.4-1992) the MAP for the .308 Win is 62 000 PSI, the mnimum proof Pressure is 83 000 PSI and the Max. Proof Pressure is 89 000 PSI.
Then CIP, in the TDCC they state (for the .308 Win again);
MAP of 4150 bar (60 175 PSI), a PK (max static pressure) of 4773 bar (69 209 PSI) and a PE (average proof test pressure) of 5190 bar (75 255 PSI). They also provide a minimum energy level for the poof test, EE of 3920 Joules.
The difference between both CIP and SAAMI datas looks big but in fact it is not, both standards using different methods of measuring (location and transducers) the pressure. Norma published their .308 Win loads as being in the 49 000 PSI.
If it's curiosity that drives you, have a look to this (hope you understand swedish, though) http://www.testfakta.se/Article.aspx?a=16439
And for more graphic stuff, look at this; http://www.testfakta.se/Article.aspx?a=16350
As you will see in there, if the pipe is clogged, it is this part (the barrel) wich will fail (Browning and Remington deplorably failed at this test), not the action.
Give us a better explaination of what you have in mind and it will be easier to bring you to the right information.
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RSI pressure trace is now back in stock if you would like to know your chamber pressure:
http://www.shootingsoftware.com/pressure.htm
Got the e-mail today, they're accepting orders again.
http://www.shootingsoftware.com/pressure.htm
Got the e-mail today, they're accepting orders again.
- Location
- Calgary, AB
OK, paying strict attention to symantics would mandate that the nominal "Rated Pressure" for a barrel for unlimited service (cumulative number of rounds fired) would default to the published SAAMI service pressure specification limits.
Boomer has an excellent post on this.
From a more practical point of view, the issue is not so much the rated pressure of the barrel, but the pressure of the load you have in your barrel. It is not sufficient to stick to the loads in the loading manual.
Their loads might be too hot or too mild in your rifle.
A good approach is to use the loading manual to suggest appropriate powders for your bullet, and then work up a load, testing for accuracy, extraction/ejection and pressure signs. Once you have reached the maximum velocity the book shows for a similar length barrel (if you reach it before getting prssure signs) then stop. There is no free lunch. more velocity means more pressure.
A well made rifle (most custom rifles and a few production rifles) will easily far exceed max pressure before showing pressure signs such as sticky extraction.
Some rifles (Remington comes to mind) will need more powder than the book maximum to get to the max velocity because of the chamber design. The key to all this is a Chrony to monitor velocity. Velocity is closely related to pressure, assuming the right powders and good brass.
The comments above mentioning the published pressure maximums of US ARMY, SAAMI and CIP are correct, but all three are based on different measuring systems. The US ARmy specs are based on CUP, although they refer to the units as psi. Civilians distinguish between the two systems by using cup units and psi. As it happens, 50,000 cup for 7.62 and 62,000 psi for 308 are about the same pressure.
The SAAMI and CIP systems are different, but the numbers are close together.
From a more practical point of view, the issue is not so much the rated pressure of the barrel, but the pressure of the load you have in your barrel. It is not sufficient to stick to the loads in the loading manual.
Their loads might be too hot or too mild in your rifle.
A good approach is to use the loading manual to suggest appropriate powders for your bullet, and then work up a load, testing for accuracy, extraction/ejection and pressure signs. Once you have reached the maximum velocity the book shows for a similar length barrel (if you reach it before getting prssure signs) then stop. There is no free lunch. more velocity means more pressure.
A well made rifle (most custom rifles and a few production rifles) will easily far exceed max pressure before showing pressure signs such as sticky extraction.
Some rifles (Remington comes to mind) will need more powder than the book maximum to get to the max velocity because of the chamber design. The key to all this is a Chrony to monitor velocity. Velocity is closely related to pressure, assuming the right powders and good brass.
The comments above mentioning the published pressure maximums of US ARMY, SAAMI and CIP are correct, but all three are based on different measuring systems. The US ARmy specs are based on CUP, although they refer to the units as psi. Civilians distinguish between the two systems by using cup units and psi. As it happens, 50,000 cup for 7.62 and 62,000 psi for 308 are about the same pressure.
The SAAMI and CIP systems are different, but the numbers are close together.
- Location
- The Conservative part of Ontario
Barrels from different manufacturers, even within one manufacturers stock, have many differences.
From the basic wall thickness, through to chamber variances. Many many differences. Even the steel used will have variances.
I'd be very hesitant to say that based on one barrel, another will be the same.
The best advice in this thread so far, is to use published data, and don't exceed maximums.
Sure it can be done, (exceeding maximums) and some of the more experienced reloaders here have done it, however, that doesn't make it a smart thing to do.
When you strike out on a project like that, you are on your own. Others can tell you what they have done, but beware, it may not, probably will not, be the same if you try it.
From the basic wall thickness, through to chamber variances. Many many differences. Even the steel used will have variances.
I'd be very hesitant to say that based on one barrel, another will be the same.
The best advice in this thread so far, is to use published data, and don't exceed maximums.
Sure it can be done, (exceeding maximums) and some of the more experienced reloaders here have done it, however, that doesn't make it a smart thing to do.
When you strike out on a project like that, you are on your own. Others can tell you what they have done, but beware, it may not, probably will not, be the same if you try it.
Your question goes to the heart of reloading,the safe pressure.Even old WWI rifles usually are good to over 100,000 psi.And it's the actions that give up first.So barrel stength is not the limiting factor,nor is the bolt action. It's the yield strength of the brass case.Those who have done experiments on case expansion vs pressure suggest it can be as high 80,000 or more. This will vary with brand and even lot #. Before you say yea-hay,here's a story from Ken Howell,an expert on handloading. He didn't say names,you can get sued,but you can guess. A rifle owner only shot the rifle company's ammo.Back then they were truly red-lined,as they had no SAAMI to answer to.They were famous for their velocity. Metal fatigue set in and the bolt lugs sheared off.
I don't think you want bolt-in-the-eye,so we back off there,too. Modern rifles are chambered in cartridges from the mild 257Roberts to the latest wizzum magnum.And that's were we will get our max.65,000psi.But notice the words modern rifle.If a new reloading manual lists 3100 for that wizzum magnum,that's sure as heck is max.But if it's a 30-06 and if there're 180 Accubonds and you are loading RL-22,you can pass the 2700,up to a max of 2800 and still be under your 65,000,but over the 60,000.
I don't think you want bolt-in-the-eye,so we back off there,too. Modern rifles are chambered in cartridges from the mild 257Roberts to the latest wizzum magnum.And that's were we will get our max.65,000psi.But notice the words modern rifle.If a new reloading manual lists 3100 for that wizzum magnum,that's sure as heck is max.But if it's a 30-06 and if there're 180 Accubonds and you are loading RL-22,you can pass the 2700,up to a max of 2800 and still be under your 65,000,but over the 60,000.
Just a bit of clarification. The measurements of steel tensile strenght you mention are for a sample of steel only, not the stresses put on a barrel when fired.
You mention a steel with a tensile yield of 120,000 psi. That is NOT THE SAME AS a 60,000 psi (120,000 psi) CHAMBER PRESSURE measurement.
The greater thickness of steel around the bore spreads the stress and reduces the AVERAGE stress applied to the steel in the barrel.
