Saami pressure

spas12

January 16, 2012 21:00

I think they're both 65k psi

0

tsr1965

January 17, 2012 00:50

Hawkshaw,

here is the link to SAAMI's website. Help yourself.

http://www.saami.org/specifications_and_information/publications/download/205.pdf

I have reviewed several pieces of data, and cannot find the 460 S&W anywhere. It leads me to believe that this cartridge might not be SAAMI listed. The 454 Casull has a maximum of 65,000 PSI.

Best

EDIT 1

quote:So if .454 and .460 use the same caliber bullets and are loaded to the same max operating pressures why is there a difference in performance? I think its two things:

a. "Real" .454 loads are quite a handful, and so in practice most commercial .454 loads aren't loaded to their max potential. Putting a .454 into a really heavy gun with a compensator goes a long way towards taming the recoil.

b. Since pressure is inversely proportionate to volume, the larger case volume of the .460 means you can cram in more powder yet still get the same maximum pressure.

The real answer is, that the elapsed time that the 460 is at that pressure is longer than the 454. Almost like short swinging a baseball bat for a base hit, versus a good follow thru for a Home Run. The longer the dwell time, the more energy is applied to the projectile. But yes, the 460 does hold more slow burning powder...you just need the barrel length to use it.

Best

EDIT 2 quote:The reason the curve is more advantageous with the .460 is the larger case. If the cases were the same volume, since max pressures are the same, you could simply replicate any .460 load in a .454.

But this is not the case, and that is why we have the 460 S&W, so we have that extra capacity, to provide that extra time under the pressure curve. That extra capacity is the same reason Mr. Casull developed the 454, to have more power than the 45 Colt. quote:Barrel length is important in determining final velocity, obviously, but its mostly irrelevant to peak pressure which occurs before the bullet leaves the barrel.

Since the best .460 rounds go faster than .454 ones from the same exact gun, its fair to say that barrel length isn't what's making the .460 go faster! Its hotter loads.

As in how anything goes for speed, there is no replacement for cubic inches. The bigger the displacement, the faster we go.

However, in modern firearms, the terms overbore, and efficiency come into play, not with just rifles, but also with handguns, and revolver's too. For any given barrel length, the 300 RUM is going to outpace the 30-06, or the 460 will outpace the 454. However, the longer the barrel is, to contain the time under the pressure curve, the higher the difference in velocity between the two cartridges will be. At some length, will come the top efficiency of the 454, but the top efficiency from the 460 will have a longer barrel. The given factor here would be the use of the same propellant's.

As you also know, ones modification of the pressure curve starts, but does not end with the selected propellant. The burn rate of the propellant, bullet weight, and size of the combustion chamber all play a very important part of efficiency. However, barrel length, to the knowledgable loader, will help him determine what propellant to use.

Best

0

beantownshootah

January 17, 2012 06:11

SPAS12 has it right.
The max operating pressure for .460SW is 65,000 PSI; same as for the .454 Casull.

You can check the reference here, and its a good overall article on the gun and caliber:
http://archives.gunsandammo.com/content/sws-riflerange-revolver'
quote:
The .460's straight-wall 1.80-inch case employs a Large Rifle primer to deal with the heftier charge. \The maximum average pressure of the .460 is 65,000 psi--5,000 psi more than the .500 S&W's pressure limit and equalling several .300 magnum-class rifle cartridges.

I like this bit:

quote:Shooting the .45s out of the X-frame can best be compared to shooting .38 wadcutters out of a large-frame .357. Shooting the .454s? About like shooting 125-grain mags out of a medium-frame .357. Nope, the X-frame doesn't exactly turn the .454 into a recreational plinker. But it comes closer than you'd expect.

So if .454 and .460 use the same caliber bullets and are loaded to the same max operating pressures why is there a difference in performance? I think its two things:

a. "Real" .454 loads are quite a handful, and so in practice most commercial .454 loads aren't loaded to their max potential. Putting a .454 into a really heavy gun with a compensator goes a long way towards taming the recoil.

b. Since pressure is inversely proportionate to volume, the larger case volume of the .460 means you can cram in more powder yet still get the same maximum pressure.

Edit:
quote:The real answer is, that the elapsed time that the 460 is at that pressure is longer than the 454. Almost like short swinging a baseball bat for a base hit, versus a good follow thru for a Home Run. The longer the dwell time, the more energy is applied to the projectile. But yes, the 460 does hold more slow burning powder...you just need the barrel length to use it.

To be really precise, what matters in determining bullet velocity is the total area under the curve of chamber pressure vs. time. That curve represents the sum total of force pushing the bullet out of the barrel. Its not just the duration of the peak pressure, and its a slightly different thing than dwell time.

The reason the curve is more advantageous with the .460 is the larger case. If the cases were the same volume, since max pressures are the same, you could simply replicate any .460 load in a .454.

For a more simple explanation, Boyle's law states that pressure of a gas is inversely proportionate to the volume its in. If you increase the volume of a cartridge, with the same amount of powder and same caliber bullet, peak pressure will go down. Same gas in larger volume cartridge = lower pressure.

Now if you want to achieve the same peak pressure again, you have to add more powder. If so, you're driving the same bullet with more powder and you get more velocity. Again, a bigger case potentially lets you cram in more powder without increasing peak pressure.

Barrel length is important in determining final velocity, obviously, but its mostly irrelevant to peak pressure which occurs before the bullet leaves the barrel.

Since the best .460 rounds go faster than .454 ones from the same exact gun, its fair to say that barrel length isn't what's making the .460 go faster! Its hotter loads.

0

v35

January 17, 2012 09:16

Thanks for the current SAAMI ref. Mine is 1984.

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