I got a B in Physics in school, so I am not an expert. But, does it bother anybody to see cartridge that are about the size of a thimble shoot heavy for caliber bullets at 4000fps?

I read often about guys shooting little cartridges like the 6,5x47 with 140gr bullets at velocities I couldn't reach with my old .256 Newton.

Isn't pressure pretty high?

First, recognize that you can't believe everything you see on the net. Some people lie and some people just have no clue so they guess.

Having said that the pressure in a firearm is dependent on the amount of gas, the speed at which it expands due to the heat of the powder and the area in which it expands. There is a range of powders the will make a certain amount of pressure in the "average" chamber with a "normal" throat and a given bore / groove size combination and an optimum finish.

A longer throat will lower pressures as will a loose bore or worn lands. All the variables mean that it is unlikely that you will get the same pressure and velocity in any two guns firing the same load.

There is also a point where more pressure will not provide more velocity. At that point the pressure rise is so fast that the bullet has no time to accelerate and destruction of the gun is very close. Some people load very close to that point without comprehending what damage they are doing. Few of us have the testing equipment and skill required to test the pressure curve in our firearms so some people have no clue what they are doing or what they are achieving.

Those folks are guided by "wishful thinking" and supposition.

Julian S. Hatcher wrote what is still to me the definitive work on pressure as a part of his "Hatcher's Notebook". While it specifically dealt with pressure testing to destruction the Springfield '03, I still believe it is the most thorough pressure testing and explanatory writing ever done.

Now; having said all that, if memory serves, Hatcher determined that Springfields held proof loads of 75kpsi quite well, and came apart only at pressures about 100kpsi. Today's receivers are every bit that strong, if not stronger. Finally, it goes without saying that the weakest link is the cartridge case itself...

There are those out there that will approach the threshold of "energetic disassembly" in the never ending belief that "faster is better". It is, in my mind, a fool's errand.

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I read often about guys shooting little cartridges like the 6,5x47 with 140gr bullets at velocities I couldn't reach with my old .256 Newton.Isn't pressure pretty high?

It scares the heck out of me when I read some velocity claims posted on various sources. Many others like you make me scratch my head and wonder HOW. Heck many could be ohnest mistakes with their Chrony setup. Others are wishful thinking.

Heck I had a rancher in W TX for years that claimed his 264 with deer weight bullets had a velocity of over 4000FPS. I gave up trying to convince him otherwise.

Bottomline there is no free lunch. You need more gas expansion and/or pressure for higher velocity.

Don't forget the Newton was loaded in the 50,000 range I believe not 63,000 like the 6.5x47

How many of you have proper pressure measuring equipment ??
Does the bullet come apart in the air ,in the animal , or does it do what it's designed to do ?

The 6.5x47 has a pressure rating of 63090 psi Piezo measurement.

The original pressure rating for the 256 Newton in the mid-1910s was 52000 CUP measurement, same as the 30-06 parent cartridge. The current SAAMI rating for the 30-06 is 62000 psi Piezo measurement; which would be the modern equivalent for the 256 Newton.

That said, in a commercial action using high quality modern brass there is little reason to not believe a 63000 psi Piezo loading in the 256 Newton to not be safe. Heck, your firing 270 Winchester cartridges from the same action and the 270 Winchester is loaded to 65000 psi Piezo measurement.

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The original pressure rating for the 256 Newton in the mid-1910s was 52000 CUP measurement

What I get for believing or maybe not being able to read QL.

Today's rifles are many times stronger than a single heat treated 1903 Springfield. Remember, pressure is self limiting in rifles by the primer; it will act as a safety valve and let you know you are in trouble before you really are. As long as we have to use brass cases and brass primers, we can't shoot anything above about say, 70000 psi, and even then your brass will not last very long. Look at our 120mm tank cannon; operates at over 100K psi, BUT, with a steel, electric primer that is screwed into the cartridge case (which is only a few inches long; pressure is held with a rubber seal). So yes, guys might be using high pressure but not so high that the rifles won't take it. The primer will fail first.

You'd be amazed how magically you can reach previously unheard of velocities, as verified by a chronograph. All you have to do is fudge the chronograph screens a little closer together. Rounding "up" also helps.

ISS

You can check both chemistry and physics books for the pressure vs volume relationships.

one is PV=nRT
http://en.wikipedia.org/wiki/Ideal_gas_law

The other is PV=PV

You do not get anything for free.
There is no magic for velocity. It takes pressure. The more velocity the more pressure required.

quote:

Originally posted by SR4759:
ISS

You can check both chemistry and physics books for the pressure vs volume relationships.

one is PV=nRT
http://en.wikipedia.org/wiki/Ideal_gas_law

The other is PV=PV

You do not get anything for free.
There is no magic for velocity. It takes pressure. The more velocity the more pressure required.

In a gun there is a lot more to the pressure / velocity relationship than the physics of a "standard model".
In a rifle you are not working with a constant pressure because as the powder burns the pressure rises in a non-linear curve. The projectile (piston) is designed to deform and it is riding in a rifled bore that can vary a great deal from one barrel to the next. The heat from the burning powder and the pressure wave front that it causes adds to the pressure peak and rapidly drops off to less than 10% of the peak pressure.
It is the amount of pressure and the time/pressure curve that makes the velocity in a gun. It is easy to get 60000 psi in a 3006 using HP-38 powder but it will give a lower velocity than a 50000 psi charge of H4895.