Max Pressure (I don't get it)
- Thread starter Shakky
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270's were built on newer rifles with better steels than early 30-06's. Pressure isn't always just A mechanical reading. - dan
A chain is only as strong as its weakest link and the SAAMI regulates the chamber pressure for the oldest and weakest firearm the cartridge will be fired in.
Meaning in a new rifle like a Remington 700 the rifle could be loaded to the same pressure as the .270 Win.
Meaning in a new rifle like a Remington 700 the rifle could be loaded to the same pressure as the .270 Win.
it's not the brass that contains the pressure but the chamber and bolt.
This. Brass is just a seal for the gases more or less. The steel barrel and bolt take the brunt of the force.
Think about the 45-70. Early loadings with smokeless powder were a 405gr bullet at 1400fps, whereas with a modern lever action you can push that same bullet at more like 2000fps, and with something like a Ruger #1 you can push it even faster. The SAAMI specs are what they are, but that doesn't mean it can't be loaded hotter if you know what you are doing.
Another example is the 6.5x55. There are a lot of swedish mausers from the early 1900s floating around, and so most 6.5x55 ammo is loaded to pressures that would be safe in those rifles. But if you go buy a modern bolt rifle you can load it hotter without issue.
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Apparently different cartridge designs have higher or lower swings in pressure. Cartridges that have higher swings in pressure have to have a lower max allowable pressure. I believe 243 win and 7mm rem mag are two cartridges that had their max allowable pressure lowered over the years because of more accurate pressure testing.
metallurgical engineers set a safe working pressure for the materials involved based on good engineering practice and experience. A "safety actor" is used for setting safe working limits.
As an example, If a particular rope is loaded to failure and it breaks at 10,000 lbs, what can the safe working load be? 9,999 lbs? No that would be too close. How about 1000 lbs which would be a safety factor of 10. Because the rope may be subjected to dynamic loading (a jerk), differences in the rope diameter during manufacture, normal wear and tear etc. Different types of ropes have different safety factors and for the intended use.
Rifles are built with different actions, some old and some new, variances in chamber headspace, actual steel differences, the list goes on and on. Setting these "safe pressures" for any rifle out there requires a safety factor that will be safe for us to use. Vast experience in the field of metallurgy is required these limits, which are not set by lawyers as some on here think.
As an example, If a particular rope is loaded to failure and it breaks at 10,000 lbs, what can the safe working load be? 9,999 lbs? No that would be too close. How about 1000 lbs which would be a safety factor of 10. Because the rope may be subjected to dynamic loading (a jerk), differences in the rope diameter during manufacture, normal wear and tear etc. Different types of ropes have different safety factors and for the intended use.
Rifles are built with different actions, some old and some new, variances in chamber headspace, actual steel differences, the list goes on and on. Setting these "safe pressures" for any rifle out there requires a safety factor that will be safe for us to use. Vast experience in the field of metallurgy is required these limits, which are not set by lawyers as some on here think.
Yeah like my lee enfield i have chambered in 32 S&W. I could double the max pressure for that round and still be safe, but that round was made for small handguns about 125 years ago. So they have to have pressure set for the weakest fire arm that was chambered in said round.
This isn't a hard and fast rule. For instance, you can buy plenty of 45-70 ammo that is not safe to shoot in a trap door springfield. Some also question the safety of using modern 6.5x55 ammo in Norwegian Krag rifles. Or modern 30-06 in an M1 Garand. Im sure there are others, but you get the point.
^^ Right, my brain went out to lunch for that post, i mostly only have obsolete calibers, old rifles and reload for them, i forgot all about modern advances in old rounds when posting that. i even use trapdoor 45-70 data for my 71/84 Mauser loads, Ruger no1 data would blow the rifle apart
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Modeled as an open ended cylindrical pressure vessel. The chamber pressure developed by the expanding propellant creates stresses and strains in the steel which need to be limited so that the steel springs back to its original dimensions after each shot (i.e. stresses kept below the yield strength of the steel).
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This applies to the rifles, but not necessarily the ammunition. Ammunition makers must decide how hot to load their cartridge that will be sold to the general public, and the general public might have a different variety of rifles of varying strengths.
That's where SAAMI comes in. The members of SAAMI set maximum pressure standards for the ammunition, not necessarily the rifles. The SAAMI maximum pressure for a given cartridge will be set by considering the rifles that it will be shot in and their relative strengths. Cartridges that were developed in 1905 will also be shot in some rifles that were built in 1905. A cartridge that was developed 30 years later in 1935 would only be used in rifles with metallurgy that would be no older than 1935, and metallurgy had advanced a great deal between 1905 and 1935. The steel used in the 270 Winchester rifles was better than the steel used to make 30-06 made 30 years earlier.
That's why the 30-06 and the 270 cartridges have different SAAMI pressure standards. It does depend on what rifle it MIGHT be used in. A reloader who knows what they are doing could safely load his 30-06 to 270 Winchester pressure levels if the rifle he loads for is made from modern steel.
...it's a bit more complex
...materials play a part, but only in what they can stand up to
...each cartridge has its own specs moreso because of its size and shape...straight wall/angled wall, shoulder/no shoulder, shoulder slope/no shoulder slope, sharp shoulder, etc all determine the pressure a cartridge is capable of developing...and then the size of the cartridge itself...and the bullet diametre...christ, they don't come up with these sitting around in the morning at the breakfast table off of secret codes on cereal boxes...
...materials play a part, but only in what they can stand up to
...each cartridge has its own specs moreso because of its size and shape...straight wall/angled wall, shoulder/no shoulder, shoulder slope/no shoulder slope, sharp shoulder, etc all determine the pressure a cartridge is capable of developing...and then the size of the cartridge itself...and the bullet diametre...christ, they don't come up with these sitting around in the morning at the breakfast table off of secret codes on cereal boxes...
The No.1 Enfield rifle was made from softer steels than the No.4 Enfield rifle that was later chambered in .308/7.62.
The commercial .303 British ammunition is loaded to the oldest and weakest Enfield rifle it will be fired in.
Meaning factory ammunition is loaded to the weakest design rifle it will be fired in for safety. This is approximately 38,000 cup or 43,000 psi and equates to 16.5 to 17 tons using the older British pressure standards.
Below is from the 1929 British Textbook of Small Arms, the British used the base crusher system of measuring chamber pressure. A hollow copper crusher was used at the base of the case that allowed the firing pin to pass through. The case had to be oiled to measure actual chamber pressure and if not oiled it measured much less. This pressure on the bolt face is called bolt thrust which over time causes the headspace to increase. The British military to this day use two oiled proof pressure cartridges to proof small arms, and if the headspace increases over a given amount the rifle fails proof testing. On the No.1 Enfield rifle if the headspace increased .003 or more during proofing it it failed proof testing due to lug setback.
Bottom line, my Remington 760 Gamemaster chambered in .270 Winchester was rated at 65,000 psi. "BUT" the same 760 in 30-06 fired ammunition rated at 60,000 psi.
Now ask yourself how warm you could load a new Remington 700 in 30-06 bolt action like the chart I put in my first posting. On the flip side of this I would not load a WWI made 03 Springfield 30-06 or M1 Garand on the warm side.
As a side note I do not load any of my firearms above the maximum rated load and the majority of my reloads are mild mid-range loads that are easy on my brass.
The commercial .303 British ammunition is loaded to the oldest and weakest Enfield rifle it will be fired in.
Meaning factory ammunition is loaded to the weakest design rifle it will be fired in for safety. This is approximately 38,000 cup or 43,000 psi and equates to 16.5 to 17 tons using the older British pressure standards.
Below is from the 1929 British Textbook of Small Arms, the British used the base crusher system of measuring chamber pressure. A hollow copper crusher was used at the base of the case that allowed the firing pin to pass through. The case had to be oiled to measure actual chamber pressure and if not oiled it measured much less. This pressure on the bolt face is called bolt thrust which over time causes the headspace to increase. The British military to this day use two oiled proof pressure cartridges to proof small arms, and if the headspace increases over a given amount the rifle fails proof testing. On the No.1 Enfield rifle if the headspace increased .003 or more during proofing it it failed proof testing due to lug setback.
Bottom line, my Remington 760 Gamemaster chambered in .270 Winchester was rated at 65,000 psi. "BUT" the same 760 in 30-06 fired ammunition rated at 60,000 psi.
Now ask yourself how warm you could load a new Remington 700 in 30-06 bolt action like the chart I put in my first posting. On the flip side of this I would not load a WWI made 03 Springfield 30-06 or M1 Garand on the warm side.
As a side note I do not load any of my firearms above the maximum rated load and the majority of my reloads are mild mid-range loads that are easy on my brass.
a bit of that is correct but some of it is backasswards.
Cartridge pressure specs are set in fairly simple manner, based roughly on the strength of the rifles that it will used in. The pressure standards are not set to take into account the shape of the cartridge< but if that is so, then somebody please explain why the 264 win mag and 458 winmag have basically the same pressure rating. The answer is that pressure is pressure, regardless of shape.
The shape of the cartridge will most defibnitelky influence the ENERGY that the cartridge will pass on to the bullet, and the bullet will most definitely influence pressure, so each cartridge must be loaded appropriately.
But 70,000 psi on a 458 winmag is the same as 70K psi on a 264 wimnmag.
The limiting factor is ALWAYS the strength of the materials. The pressure is ALWAYS regulated by the load, not the other way round.
