.357 Mag SAAMI vs. CIP

[ligonierbill]

Starting to load .357 Mag again, this time for a 4" GP-100. I found some Hornady 125s and 140s, and I was set to go with H110. Have their manual, and just for fun, I checked Quickload. Something I didn't know: CIP spec for this caliber is 3,000 bar or 43.5 ksi. That's 24% higher than SAAMI's 35 ksi! Sure enough, QL calculates Hornady's book max loads (19.9/125 and 18.4/140) at just under SAAMI max. With H110, that's also a full case, so much more is impractical anyway. However, I have some AA#9 on hand. QL suggests it might be a better powder for these light bullets, if one were to load to, say, within 1,500 psi of CIP. I presume the European manufacturers load their ammo based on CIP. Comments? (Other than, "Try it and let us know.")

 

[SL1]

The older US manuals had loads of the older powders for the older bullets based on CUP measurements. For the most part, they were higher charge weights giving higher actual pressures and higher measured velocities.

But, a lot of verbal smoke screens have been constructed around the variabilities in primer lots, powder lots, different test guns, and the differences in the psi and CUP measurement systems. For a while, there was a tendency to try to claim that 35,000 psi is equivalent to 46,000 CUP in the .357 Magnum cartridge. But, that is obviously not true when you consider the bulk of the loading data as one data set and analyze it.

Your GP-100 was built to the old CUP standard, and should be safe enough with the loads from the old manuals with the bullets and primers that those manuals used. However, when trying to substitute bullets, there are some things that those old manuals did not address, like solid copper bullets.

But, since Hornady's manual #4 (1991) thinks that it is OK to put 14.3 grains of #9 under a 158 grain XTP and its #8 manual (2010) reduces that to 11.5 grains (using different brands of standard strenght primers), you can bet that the 14.3 grains is going to be above 35,000 psi, but below 46,000 CUP. Interestingly, H-110/W-296 give LOWER velocities than AA#9 in the old manual, but higher velocities than AA#9 in the new manual. That is because a case full of the slower powders did not reach 46,000 CUP (it was about 39,000 CUP) but the case could hold enough of the faster AA#9 to reach higher pressures.

SL1

 

[ligonierbill]

That 'I' is not a typo. CIP = Commission Internationale Permanente, the authority that sets European firearms standards. That's my reference, not Copper Units of Pressure. Many calibers differ to a degree, but I was surprised at the difference for .357. CIP standards are based on proof tests, not conversions from any other system. However, your numbers track Quickload safe loads under CIP standards. Sounds like the old manuals show what Quickload does: AA#9 is the better powder for light bullets.

 

[DWFan]

Old vs. New

For the .357, simply download Accurate Arms V3-2 and V3-3 .pdf files. The 3-2 has the old cup data, the 3-3 has the new psi data. The difference is obvious. For a 125gr Nosler JHP and a 6" barrel...
(New) 15.6gr of AA #9...1567 fps...35,178 psi
(Old) 17.0gr of AA #9...1685 fps...45,100 cup
In fact, the 15.6gr maximum load of the SAAMI PSI data is only .3gr above the starting load for the old CUP data.

 

[ligonierbill]

Thanks for the feedback. I am not above pushing the limit a bit, but in this case I'm going to stay with current SAAMI standards. My purpose in loading 125s here is to see for myself how the classic .357 Mag stacks up against the upstart .357 Sig. Current standard = level playing field. I'm just curious about those European specs. In the field, I will normally load heavier bullets, and it does seem that the .357 Mag really comes into its own there.

 

[mehavey]

CIP, SAAMI and CUP are not only different, they are measured differently.
See Testing Firearms: Measuring Chamber Pressures for a reasonably concise explanation.

This has caused untold number of screaming & yelling headaches when comparing SAAMI to NATO/"military" pressures for military cartridges, esp in the great .223 vs 5.56 what'sacceptablepressure debate. When all the dust settles, the stress that the case goes through is roughly the same for either SAAMI or CIP numbers, it's just that that pressure test was run differently and therefore came up w/ different numbers -- for near if-not-the identical load.

In the OP's case, the GP100 is built like a proverbial brick [expletive deleted]house. Don't much sweat it until the cases start getting sticky on extraction.

 

[wncchester]

The end goal of all the max pressure cartridge specifications is to put the same level of stress on the firearm. It matters not if it's SAAMMI or CIP, nor if its read in CUP, PSI, Atmospheres/BAR, mm of mercury or water column; if a max load is safe according to one system it's safe for all firearms in good condition. Ditto the reloading info.

Given the low BCs of handgun bullets and the hottest vs norrnal speeds it's hardly rational to push the limits; take a long step closer and the terminal speed will be about as different in effect at the target.

 

[SL1]

ligonierbill,

Sorry I didn't get back to this for a while.

Hopefully you have realized by now that I did NOT confuse "CIP" and "CUP". "Copper Units of Pressure" is a term adopted by SAAMI for its older standards when it was realized that copper crusher pressure measurement systems did not match the newer electronic pressure measurment systems in terms of peak presssure. So, to distinguish the results of the two systems, CUP was adopted for the results of the old system. But, manuals printed before that time said "psi" when they were actually reporting the results of copper crusher measuring systems. So, there are really three standards represented in reloading manuals:

SAAMI old = 46,000 CUP
SAAMI new = 35,000 psi
CIP = 3,000 bar = 43,511 psi.

One thing to watch about the different versions of Accurate Arms data for their #9 powder in the .357 Magnum is that the old data (which is measured in CUP) was shot with standard strength primers, while the newer data was shot with mangum strength primers. The magnum primers will give higher peak pressure and therefore result in lower max charge weights and lower velocities.

So, it is really hard to find apples-to-apples comparisons between old and new SAAMI standards for the .357 Magnum. The data I provided from Hornady is the closest that I have found.

While many will dispute it, there is an obvious lower performance level for the new SAAMI standard compared to the old SAAMI standard for the .357 Magnum and .44 Magnum cartridges.

SL1

 

[crowbeaner]

125 grain Speer HP 18.5 of H110/WW296
140 grain Speer HP 17.5 of H110/WW296
158 Speer HP 16.6 of H110/WW296

FC nickel brass, CCI 550 primers. I recommend you use a tight neck tension and a firm crimp in the crimping groove. I've shot these in every 357 I've owned and never had a problem.

 

[ligonierbill]

Thanks all for the replies. Unless SAAMI sets a particularly weak standard (e.g. 6.5x55) I try to stay within it. Yes, I think they "dumbed down" the .357 Mag, but it's still a great round at that. Someone can always get another 100 fps. Ammo makers do with custom powders. I could with a few more grains of AA#9 and still be within somebody's spec. But no need. If I need to crush something, I've got this .45 Colt Blackhawk (even the load manuals toss the spec for "Ruger only"). If that's not enough, I can talk myself into one of those pretty Freedom Arms cannons (not hard to do).

 

[57K]

ligonierbill, the CUP system may seem old and outdated, but that doesn't stop Lyman from using it where their warmest load with a 145 gr. SilverTip in .357 Magnum produces 44,800 CUP. 46,000 CUP is the older pressure standard with 35,000 PSI being the newer SAAMI Max. Average Pressure, or MAP. It is also possible to conduct CUP and PSI SAAMI testing simultaneously because both pressure testing methods are done at the same location in the chamber. CUP and SAAMI PSI also reverses in value with magnum revolver rounds compared to rounds like the 9 x 19mm where the equivalent PSI SAAMI MAP is 33,000 CUP/35,000 PSI. In the .357 Magnum, 35,000 PSI pressure loads tend to produce more than 40,000 CUP.

IMO, the CIP PSI method is the best used with the piezoelectric transducer placed forward of the case-mouth and looks closer at Peak pressure rather than average chamber pressure. I once got a very thorough explanation on this from Johan Loubser who used to be Accurate and Western Powder Co's. ballistician. He felt that the CIP system would eventually replace the SAAMI system in the US, but since that conversation, there's been a kind of resurgence in CUP testing, even with it being the least reliable overall.

I've done a lot of reloading with European powders like V-V and NobelSport/Vectan that were pressure tested in the CIP system and Vectan data also gave ratings in BARs which I was already familiar with from calculating hydraulic pressure in my design work. As was stated correctly earlier, it really doesn't matter which system is used because a Max. load is a Max. load regardless of the pressure system. So, 35,000 PSI SAAMI magnum revolver loads may be warmer than some may think, and CIP allows a slightly higher PSI value because of the different location of the transducer. I have and still use V-V 3N37 as well as data from the early 90's #2 load guide where the 9mm was loaded up to 36,300 PSI/CIP and closer to the former 9mm pressure max. of 35,700 CUP wherein today's SAAMI +P rating of 38,500 PSI is fairly close to the old CUP rating. In the same V-V load guide, they loaded .357 Magnum to the same pressure limit of 36,300 PSI/CIP.

 

[SL1]

57k,

The main reason that some manuals went back to the CUP system for the .357 Magnum is that it gives higher performance than loads based on the newer SAAMI psi standard.

SAAMI allowed both systems to be used, and some manual makers found that the psi standard gave loads with lower performance, so went back to the CUP system and standard for just the .357 and .44 Magnums to make their manuals more attractive to buyers.

People tend to assume (and some claim) that the two systems give the same actual max pressure. But, that is obviously not true when you compare load data (e.g., see Hornady data in the second post to this thread).

Why SAAMI down-graded the two oldest Magnum cartridges while making similar actual pressure standards for momst others has not been publicly discussed. But, any graph of psi vs CUP for a variey of cartridges makes it clear that something is different with those two.

SAAMI is a group of commercial outfits, so marketing of new cartridges may have had something to do with how they voted. And, marketing lighter, weaker guns for these well-known cartridges could also be a factor.

Someday, maybe they will come to their senses and make a +P or +P+ standard in psi that matches the older CUP standard in performance.

SL1

 

[ligonierbill]

Yep, it's still more art than science. Just to stir things a little more, how come for their 125s, Sierra and Hornady are only 0.1 grain apart on their H110 max loads and 3.4 grains (23%) different on AA #9? One is using a Colt Python, the other a Colt Trooper. Hmmm...Maybe I will break out the #9 and try those loads again.

 

[SL1]

One possible answer to you question would be different primer types? Both companies would know to use magnum primers for H-110, but some use standard primers for #9 while others use magnum primers for everything. It always pays to read the primer used in the data.

Another possibility is that the lots of H-110 powder were the same for both companies, but the lots of #9 powdwr were different. Still that should not account for a 23% difference. Maybe that AND the primers?

One thing that should NOT cause the difference is the gun used to measure the velocities. The pressures are worked-up in a test barrel that should be pretty close to the same for both companies. But, those barrels typically give higher velocities than commercial handguns, so the manuals often shoot the start and max loads through a sample commercial revolver and report those velocities instead of the test barrel velocities, so that handloaders get realistic expectations from reading the manual to select a powder.

SL1

 

[WESHOOT2]

Explore "proofing" of handguns under the CIP system.


Data changes because testing adds new knowledge to 'old' loads.....

 

[Clark]

John Bercovitz's Feb 11, 1993 post on rec.guns.
https://groups.google.com/forum/?hl=en&fromgroups#!msg/rec.guns/S_dalM1NJe0/cBSU4bR2jz8J
Snipping out lots of math:

The cartridge case's outside diameter is equal to about .48 inch after the cartridge has been fired. So its springback, if made from CDA 260, is .004 inches/inch (from above) * .48 inch = .002 inches diametral which of course is just the amount the chamber contracted so we've just barely got an extractable case when chamber pressures hit 70,000 psi in this barrel. This is why the ease with which a case can be extracted from a chamber is such a good clue as to when you are reaching maximum allowable pressures. By the same token, you can see that if a chamber's walls are particularly thin, it will be hard to extract cases (regardless of whether or not these thin chamber walls are within their stress limits). A really good illustration of this can be found when comparing the S&W model 19 to the S&W model 27. Both guns are 357 magnum caliber and both can take full-pressure loads without bursting. The model 27 has thick chamber walls and the model 19 has thin chamber walls. Cartridge cases which contained full-pressure loads are easily extracted from a model 27 but they have to be pounded out of a model 19. So manufacturers don't anufacture full-pressure loads for the 357 magnums anymore. 8-(

What does it all mean?
They created the 357 mag by overloading heavy 38 special revolvers until the cases were sticky. Then they backed off a tiny safety margin. Then pressure tests were done to standardized. Years later, lighter, thinner chamber wall 357 magnums were manufactured. Their chambers were easier to stretch, and so took less pressure to reach the elastic limit of brass. Cases were hard to extract. So loads had to get wimpier.

 

[SL1]

Cases were hard to extract. So loads had to get wimpier

Or, SAAMI could have done the honest thing and made a .357 "-P" standard for wimpy guns, and left the original standard in place for the original guns. they "sort-of" did that by allowing the original CUP standard to stay available. But, the Piezo-electric measurements are a lot better, as well as faster and cheaper. So, they really should have a "psi" standard that duplicates the perfromance of the oldr "CUP" standard.

SL1

 

[Clark]

In 20 years me of reading millions of gun forums posts, the #1 must be, "Can I shoot 38 special in my 357 magnum?"

If we had 357 mag -P, it could disrupt the ecological balance of gun forums.

 

[SL1]

My father-in-law used to have an really old Colt (I think) double-action that was marked ".38" and was probably a black powder era gun. But, you could stick a .357 Magnum cartridge into it with no effort. I suspect that it was used with outside-lubed bullet cartridges, so the grooves may really have been 0.38". If so, MAYBE the 0.357" diameter bullets of the Magnum cartridge could have gotten through without letting the peak pressure get close to 35,000 psi. But, would it have stayed below 14,000 psi? I doubt it. I told him not to shoot it. The bore was pitted, anyway.

SL1