Newbie SAAMI pressure question.

[TennJed]

Ok I have what is probably a stupid question, but I was wonder something about SAAMI pressure and different calibers.

Take my Ruger Blackhawk 357/9mm convertable or a 454 casull. With both the 357 and the 9mm the SAAMI pressure is close (38k and 40k). The 357 is thought to be a more powerful round. I have no idea what the pressure limit of the gun is, but lets just say it is 60,000. Would a 60k 9mm blow it up just as easily as a 60k 357? My newbie brain tells me that the 357 is stonger so no 9mm could blow it up. My logical side tells me that pressure is pressure no matter the bullet size or powder charge.

With the 454 casull the SAAMI is 50k. So I assume that a gun chambered for the 454 can handle a little more, say 60k before to explodes. (again these figures are just for illustration). I assume that a 60k 45 colt would blow up even a Ruger Blackhawk, but if the breaking point for a 454 casull gun was 60k would a 60k 45 colt blow it up.

Last thing....PLEASE understand I am not looking to create some crazy 9mm or 45 colt rounds. I have NO INTENTION of pushing the limits like some of you may be wondering. I am just curious by nature and like to understand how things work.

Thanks

 

[918v]

It's not peak pressure but how fast it rises and how long it lasts. A 357 contains more powder and therefore more energy, so it is more likely to frag your handgun. The same applies to a 45 Colt vs a 454.

 

[243winxb]

My guess is.............

Unsupported brass will come apart on firing at normal pressures. In a chamber it would seem that the pressure would have to be over 76,000 psi?? Would the firearm remain in 1 piece, my guess is yes. Steel is a lot stronger. One major problem is not all firearms are steel. "Plastic" firearms in 40 S&W do not behave well with an over pressure loading. Plus a locked action (bolt) is a lot stronger & keeps everything in one place. On a revolver, the brass at high pressure, would be stuck in the chamber.. You can find pressure data here for proof loads >http://www.saami.org/specifications_and_information/index.cfm?page=CC 357mag proof average pressure is 50,500 psi. Why modern firearms/cartridges have many different working pressures, i do not know. It would seem all could be loaded to 40,000 psi in a steel chamber???

modulus of elasticity- Cartridge Brass-
Material is 70 copper/30 zinc with trace amounts of lead & iron , called C26000. Material starts to yield at 15,000 PSI when soft (annealed), and 63,000 PSI when hard.
Material yields, but continues to get stronger up to 47,000 PSI when soft, and 76,000 PSI when work hardened.

 

[Owen]

The problem with pressures has a lot to do with the way the gun locks up. Blowback guns (no lockup at all) will generally have a lower high pressure limit than something like a revolver with a fixed breech.

You're not going to be very sucessfull firing a .357 in a blow back gun, unless the breech block is very very heavy. 9mm, .380 and .45 (all low pressure rounds) will always have a lower peak pressure than something like .357, which is almost always fired in something like a revolver or lever gun, with either a fixed breech block, or a hefy lockup method to keep the chamber closed.

As far as the cartridge brass goes, looking at the material properties is only part of the equation. the 63ksi yield strangth applies to the material whether its a foil a few thousandths thick, or a few feet thick. Obviously a .003" foil isn't going to hold 63,000 pounds, but a 2"x2" square bar should hold 252,000 pounds before yielding.

I should go into a discussion of hoop stress here, but I'm feeling lazy.

 

[Steve C]

Maximum SAAMI pressure list

Note that the .357 magnum has exactly the same maximum pressure as the STANDARD 9mm, the 9mm +P is higher. Therefore your assumption is incorrect regarding both the strength of your Ruger and the ability of it to contain a greater pressure just because its in a 9mm case. It should be noted that most manufacturers seldom load to maximum pressure level. They load to a level somewhat below that provides the best accuracy and that has a general margin of safety since their ammo is likely to be used in a variety of guns in varied condition and quality.

The Ruger is no stronger than any other pistol chambered for its particular cartridge except in the .45 Colt. However I've seen more than on Ruger .45 Colt where someone thought Rugers where so strong you could use any overload safely and blew it up.

Firearms that are "proofed" are generally fired with loads that are 50% higher pressure than standard design pressure. Proof marks are generally found in European firearms where its required by law. Thus a .357 mag pistol should hold up to a load of about 52K psi and not fail however over loads can certainly far exceed this level.

 

[TennJed]

Thanks guys.