How does SAAMI arrive at the max pressure rating for ammunition?


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1858
September 16, 2008, 08:01 PM
The reason I ask is that SAAMI specs for different calibers are independent of which rifle the ammunition is to be fired in ... right? For instance, the SAAMI spec for .45-70 is 28,000 psi regardless of which rifle is used. So how did they arrive at that? What are they basing that pressure rating on? Is it based on case separation for example? There must be a factor of safety in there too ... right?

It seems to me that any firearms manufacturer is going to look at the SAAMI specs for the caliber that they're interested in, then design the rifle to withstand pressures of the SAAMI spec multiplied by some factor of safety that they think is a reasonable compromise between cost, form, funtion, weight etc. It seems that ammunition manufacturers design their products not to exceed SAAMI specs (due to liability), but how about powder/bullet manufacturers and their reloading manuals? Would those companies such as Sierra, Lee, VihtaVuori etc contact the firearms manufacturer directly to find out the factor of safety in their specific rifle/handgun and then modify their load data accordingly?

:confused:

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bullseye308
September 16, 2008, 08:03 PM
I would guess that they have to look at all the firearms chambered in that caliber and aim for the weakest of them.

matrem
September 16, 2008, 08:33 PM
bullseye308 is correct.Handloaders with "modern" .45/70s can get "more" than most (factories) will load for it (& many other "old" calibers)
ALWAYS follow a reputable reloading manual!

Halo
September 16, 2008, 08:54 PM
Yep, for example one of my manuals (Lyman I think) has different .45-70 sections, one for old trapdoor Springfields/replicas and one for modern firearms. The load data for the latter are considerably more potent, but would almost certainly cause big problems in an old rifle.

1858
September 16, 2008, 09:01 PM
Yep, for example one of my manuals (Lyman I think) has different .45-70 sections, one for old trapdoor Springfields/replicas and one for modern firearms.

But SAAMI only lists one maximum pressure for the .45-70. SAAMI doesn't list pressures for different (newer) rifles. So how did Lyman decide what loads are safe in what rifles? Surely they would have to consult with the firearms manufactures or test the rifles themselves.

:confused:

matrem
September 16, 2008, 09:24 PM
Rifle makers can "rate"/test their own acceptable pressures.SAAMI is a "standard".
Whatever a standard is worth?

dmazur
September 16, 2008, 11:47 PM
I had a manual that listed three loads for the .45-70. Trapdoor Springfield, Lever-actions, and the Ruger #1.

I found the SAAMI site, and they are willing to part with their various publications, for a fee. I'm guessing there is more detail in this than a normal person would want to read, but it is probably the definitive source.

SAAMI publications (http://www.saami.org/Publications.cfm)

Owen
September 17, 2008, 10:12 AM
The SAAMI pressure spec is normally arrived at to ensure that older guns aren't going to get blown up with factory ammo. SAAMI doesn't care about how strong the strongest gun is, only how weak the oldest gun is.

With newer cartridges the peak pressure is usually specified by the originator of the cartridge. If I show up the the .700 owen thunderboomer, and say that the peak pressure is 65k psi, and SAAMI approves, then anyone else that builds a gun in that cartridge has to build a gun strong enough to stand up to that pressure.

The SAAMI max pressure is established so mfgs know how strong to make the gun, not the the other way around.

Steve C
September 17, 2008, 01:01 PM
From WIKIPEDIA regarding SAAMI (http://en.wikipedia.org/wiki/Sporting_Arms_and_Ammunition_Manufacturers%27_Institute) .

Jim Watson
September 17, 2008, 01:17 PM
There was not a SAAMI before there were guns. SAAMI was organized in 1926 to get all the US manufacturers on the same page. They undoubtedly standardized pressures based on what was being loaded at the time for guns being made at the time. In "modern" calibers, things haven't changed all that much. The .270 is still a high pressure cartridge by any standard and it came out in 1924, before there was a SAAMI.

As to outliers like the .45-70, I suspect that 28,000 psi was the high end that was being loaded in 1926 for rifles like 1886 Winchester. Or maybe it was what the reportedly hot smokeless USGI load produced as a transition from BP .45-70 to the Krag developed. That won't blow up a sound Trapdoor, but it won't do it any good. The usual recommendation for Trapdoor and other "group I" actions is 18,000, which is a moderate black powder pressure, such as those guns were designed for. Anybody loading heavier than 28,000 for strong guns like current Marlins and Rugers is on his own, there is no industry specification.

1858
September 17, 2008, 01:38 PM
If I show up the the .700 owen thunderboomer, and say that the peak pressure is 65k psi, and SAAMI approves, then anyone else that builds a gun in that cartridge has to build a gun strong enough to stand up to that pressure.

owen, but what would you be basing the 65ksi on? That's the whole point of my question. Is the pressure rating intrinsic to the cartridge itself so even if the chamber walls were 10" thick and the barrel walls 5" thick the cartridge would fail (in some manner) at 65ksi. Or would it be based on the failure of the rifle that you're firing the round in? Or would it be based on the maximum pressure measured when firing the "ideal" load that you developed. Do you see the point of my question?

Here's an excerpt from the SAAMI link provided by Steve C

"Under SAAMI proof test procedures, for bottlenecked cases the center of the transducer is located .175" behind the shoulder of the case for large diameter (.250") transducers and .150" for small diameter (.194") transducers. For straight cases the center of the transducer is located one-half of the transducer diameter plus .005" behind the base of the seated bullet. Small transducers are used when the case diameter at the point of measurement is less than .35".

Under C.I.P. proof test standards a drilled case is used and the piezo measuring device (transducer) will be positioned at a distance of 25 mm from the breech face when the length of the cartridge case permits that, including limits. When the length of the cartridge case is to short, pressure measurement will take place at a cartridge specific defined shorter distance from the breech face depending on the dimensions of the case.

The difference in the location of the pressure measurement gives different results than the C.I.P. standard[10]."

:)

rbernie
September 17, 2008, 01:52 PM
owen, but what would you be basing the 65ksi on? That's the whole point of my question. Is the pressure rating intrinsic to the cartridge itself so even if the chamber walls were 10" thick and the barrel walls 5" thick the cartridge would fail (in some manner) at 65ksi. Or would it be based on the failure of the rifle that you're firing the round in? Or would it be based on the maximum pressure measured when firing the "ideal" load that you developed. Do you see the point of my question?
Breechloading rifle technology back in the late 19th/early 20th century established safe load thresholds well prior to the existence of SAAMI. SAAMI simply reverse-engineered the 'hi' and 'moderate' pressure ratings and advertised them as limits.

To a certain perspective, the gunmakers found the limits of the properties of steel and brass, and created their chambering/rifle combinations accordingly. SAAMI simply makes it repeatable.

SlamFire1
September 17, 2008, 02:51 PM
If they act like any other standards group, then there are experts and recognized industry representatives on the voting side.

These people typically get together once a year and have discussions over topics of interest. They come to a consensus on what the standard says, and what it means. There are always people with agenda's, pet rocks, and the standards change based on the influence of this group and that.

I suspect that with a new cartridge, the rifle and cartridge manufacturer come to the meeting and present what they propose as maximum and mimimum dimensions, pressures, etc.

With older cartridges, I suspect they had conducted a literature search, did their best to find out what the original manufacturer had intended. Then, as with the 8 mm Mauser, just downrated the cartridge pressures because of the number of old relics they knew were floating around.

Standards get updated on regular cycles, (about every three to five years) and if you want a set, expect to pay $$$$

These groups will have some top notch experts who really understand their product and industry, and they try to set standards that are safe, and standards which do not exclude any dues paying members product.

After all, the association is voluntary, and needs dues paying members....;)

rcmodel
September 17, 2008, 02:58 PM
They also standardize chamber & free-bore dimensions.

For instance, prior to SAAMI, Colt & Winchester & Marlin all had completely different ideas about what a .32-20, 38-40, or 44-40 chamber should look like.

It still makes reloading for old guns interesting, because modern SAAMI specs make new reloading dies wrong for old chambers! So they either won't fit, or over-work the brass.

At least if you buy a new 38-40 with SAAMI spec chambers, and a new set of dies today, you can be assured the reloads will fit.

but what would you be basing the 65ksi on? That is about the maximum upper limit of cartridge brass (70% copper, 30% zinc) and still have a safety factor left over.

Brass begins to flow at slightly over 65,000 PSI, and loose or leaking primer pockets would develop, even if the entire case were surrounded with 6" of solid steel.

Since very few if any modern firearms do that, 65,000 PSI is very likely to be the upper limit until a more advanced method of containing chamber pressure is developed.

rcmodel

ranger335v
September 17, 2008, 06:20 PM
"How does SAAMI arrive at the max pressure rating for ammunition? "

Actually, SAAMI doesn't to that.

The Sporting Arms and Ammunition Manufactoring Institute is not an independant organization that dictates anything, it consists of representitives from across the spectrum of those who make ammo and guns. Sitting as a committee, they arrive at a consensus as to what various chamber pressues, velocities, chamber and cartridge dimensions for any new round will be and that becomes the SAMMI standard, not the other way around.

JustAnotherPlinker
September 17, 2008, 07:26 PM
So! It might then be possible to develop a caseless cartridge and chamber capable of pressures above 65,000 psi? Neat.

ranger335v
September 17, 2008, 11:09 PM
I said SAAMI didn't mandate anything, per se, but they aren't idiots either!

Research, test and engineering data must be presented to the board to support your claims. If not, or if the claims and data were outlandish, you would get no SAAMI sanction for the specifications you present. NOR is it likely any other manufactor would wish to ever support your project with arms or ammo. SAAMI's stamp of the group's approval is kind of important for any successful commercial gun or ammo related venture.

Factory adherance to SAAMI specs is voluntary, including the spec.s for loaded cartridges and chambers. All makers wisely try to stay as close to the tolerances, plus or minus, to maintain not only safety but their reputation in the market.

In the distant past, some die makers got kind of sloppy and made a lot of dies with worn reamers to save money. Dies made from too small reamers were too small to make good ammo. I think time and market forces eventually cleaned house and what remains in the market today is of excellant quality, across the board, no matter the brand.

Actually, for the most part, many of those sloppy older dies did a pretty good job IF the user knew what he was doing with them. But some were so bad nothing could save them! I'll just name one; did you know that Savage Arms once had a line of loading tools? I believe they had bought some small outfit and set them up, but the work quality was pretty spotty on too many items so they didn't last long.

Owen
September 18, 2008, 10:57 PM
what Slamfire says.

Companies that make guns join SAAMI. each SAAMI member get to vote at the annual meeting, which is held at The SHOT Show.

If I want to get a new cartridge approved, I submit it to the comittee a few months before the meeting. It gets reviewed by the comittee. The cartridge is presented to the meeting and they vote yeah or nay on the cartridge.

The member submitting the cartridge specifies the max pressure, with supporting data. If that cartridge is approved, then everyone who makes a gun in that cartridge needs to hold the pressure.

with current tech ammo tech, 65k is the upper limit, because much higher than that and brass flows like molasses.

cliffy
September 18, 2008, 11:37 PM
Every rifle is different in age, usage, cleaning care, quality, and strength. Notice how SAAMI always proofs to an exact 1,000 psi increment? Going 1,000 psi over will explode a rifle, I learned is not true. I've never suggested such potent loads in writing, but I've attempted higher pressures than I'd ever suggest, yet I'm still around to tell that they didn't actually explode or damage my rifle. To find one's maximum safe load, takes dedicated experimentation. Ambient temperature psi variences are never noted by SAAMI, yet it is a MAJOR governing factor. STICKING CASE hard to eject are extreme OVERLOADS; punctured primers are strong indicators of BACK the CHARGE OFF. CRATERED PRIMERS show WOW: BACK OFF on powder charges. SAAMI probably doesn't want to be sued anymore than factory loaders. NEVER GROSSLY OVERLOAD, but DO use a chronograph and commonsense in increment increases of .1 grain when coming close to maximum. ALL of my potent loads are marked under 80 degrees: over 80 degrees. Ambient Temperature is a most critical pressure factor, so what temperature are factory loads designed for specifically? Ask the factory that loaded them, cause you should want to know and they do know. cliffy

shootinstudent
September 19, 2008, 03:57 AM
ALL of my potent loads are marked under 80 degrees: over 80 degrees. Ambient Temperature is a most critical pressure factor, so what temperature are factory loads designed for specifically? Ask the factory that loaded them, cause you should want to know and they do know. cliffy

Honest question: Do you keep your rifles shaded all the time when out shooting, or is there some other way to assure the temperature of the cartridges and gun won't exceed safe limits?

Myself, if there isn't a spec for it, I won't load it.

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