SAAMI pressure derating over time

[eldon519]

In numerous articles and posts, I've read about SAAMI derating the original pressure spec of old magnum calibers such as the .357 magnum and more recently the .44 magnum. I've provided a sample of such information at the bottom of the post. I have never actually been able to locate this information from an authoritative text (a SAAMI bulletin, reloading manual, encyclopedia of cartridges, etc). A couple questions related to this topic:

Why does SAAMI derate these cartridges?

Does anyone know the timeline of the derating, especially the .357 magnum (I seen mention that it's been derated twice?)?

Would it be foolish to load to previous loading specifications in robust, modern-production weapons such as a GP100 or Marlin 1894?

Here is a sample taken from a post:
"357 Magnum original pressure spec: 47,000 PSI
357 Magnum pressure spec current SAAMI: 35,000 PSI

41 Magnum pressure spec Speer #11: 43,500 CUP
41 Magnum pressure spec current SAAMI: 36,000 PSI (40,000 CUP)

44 Magnum pressure spec Speer #11: 43,500 CUP
44 Magnum pressure spec current SAAMI: 36,000 PSI (40,000 CUP)"

Source:
http://shootersforum.com/showthread.htm?t=30815&mode=threaded

 

[918v]

Why does SAAMI derate these cartridges?

Because S&W secided to put the .357 in a K-Frame.

 

[brickeyee]

The accuracy and preciosn of ht emeasuring equipment has also gotten a lot better.

Old numbers could not have been PSI since copper crushers are not calibrated that way.
They are calibrated in CUP, Copper Units of Pressure.

The momentum of the system made accurate measurement of peak pressures sort of iffy.

With the rise of piezo systems with adequate bandwidth the true peak pressures from some old loads was found to be excessive.

 

[243winxb]

357 is 45000cup & 35000psi. SAAMI list pressures here, along with proof load data. http://www.saami.org/specifications_and_information/index.cfm?page=CC

 

[rcmodel]

Because S&W secided to put the .357 in a K-Frame.

It didn't happen with the rise in police use & popularity of the K-Frame Model 19 & 66 in the 50's, 60's & 70's.

It happened when everybody started chambering J-Frame size guns for .357.

I also agree a lot of it had to do with better pressure measuring equipment.
The old copper-crusher (CUP) method was not able to show pressure spikes of very brief duration.

Transducer (PSI) testing told them some things were taking place they had no way of knowing before.

rc

 

[243winxb]

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.

 

[Slamfire]

Would it be foolish to load to previous loading specifications in robust, modern-production weapons such as a GP100 or Marlin 1894?

In robust, modern production, modern steeled firearms, I would load as I did before.

In lightweight, pre WW2, plain carbon steel, etc, etc, I would not.


I believe the difference in pressures is due to better measuring equipment. Old copper crusher equipment did not measure pressure real time, and it did not measure peak pressure.

Having bent several pre WW2 pistols, older guns are just not as hard or as strong as later stuff. I would not hot rod a 1930's, 40's, or 50's 357. I don't know where the cut off is, but I am not hot rodding my 70's S&W's. Never saw a reason.

Now something like a Ruger Blackhawk, Super Blackhawk, Redhawk, Super Redhawk, those are very strong handguns. Exceptionally strong handguns. Massive as tanks. Never had a problem with the older full power loads. I don't like recoil so I don't shoot full power loads as much as I used to, but in these guns, I have no worries.

I still shoot a 240 Lead with 22 grains 2400, which now exceeds maximum in loading manuals, in my 1983 vintage M1894 44 Magnum. Never had a problem, don’t expect I ever will.

Sure as heck would not hot rod a 1940’s or earlier M1894 or M36. I would be nice to those.

 

[JR47]

As was mentioned, the advances in technology allow the manufacturers, and SAAMI, a more realistic definition of what pressures are actually being seen in the chambers.

It's not far different from the old velocity figures of the 20s and 30s. With advances in chronograph technology, they were found to be a bit optimistic.

SAAMI, and CIP, pressures are derived without regards for the guns that may chamber them. No guns are used to arrive at them, either. They use pressure barrels. YOU are supposed to be the final arbiter as to whether your gun is safe to use with modern loads.

Neither sanctioning body, you'll note, has anything approaching different pressures for "older guns" or "j-frames".

 

[gamestalker]

As mentioned here, the testing equiptment has become far more advanced has lead to numerous cartridges SAMMI pressures being re-established. The accurate SAMMI guidelines have actually allowed the firearm manufacturer's to build with greater confidence and accuracy regarding the pressure limits. If you look a little deeper you'll notice that many cartridges have SAMMI limits adjusted up, and down.

 

[GaryL]

I suspect the improved testing equipment has also revealed that some cartridges build peak pressure very quickly towards max loads, requiring a safety factor to account for variations in powder lots and typical charges thrown. Lyman's 49th includes a caution about pressures rising rapidly towards max loads in the 6.8 SPC. I don't think that is the only caliber with that issue.

 

[eldon519]

I'm thinking it has to be more than just better measuring instruments, because they actually changed the pressure spec, not just the load data. From what I understand, guys who were involved with the development of the .357 magnum believed that they were in the neighborhood of the high 40k psi range. For example suppose the original 1500 fps 158-gr 47,000 psi used 15.0gr of powder XYZ. New equipment comes along and reveals that you've actually been generating 55,000 psi this whole time. Well that would explain why you might have to drop published data down to 13.5gr of XYZ for maybe 1400 fps at an ACTUAL 47,000 psi, but it doesn't really explain why you would have to lower the actual pressure spec itself.

 

[rcmodel]

Another thing I have noticed over the last 55 years is the decline in quality of the guns themselves.

My old S&W's and Ruger Flattop .357's would take higher pressure and still eject easily.
Back then, chambers were hand lapped to a mirror finish, and stuck cases where just not something that happened until you got way past safe & sane load pressures.

Newer guns have less or no hand finishing done, and the chambers are not as highly polished.
Empties that fall out of the chambers on the old guns can't be ejected on many new guns.

rc

 

[amlevin]

One word----Lawyers.

and with that comes an abbeviation-----CYA

 

[Peter M. Eick]

I would agree with RCmodel on this.

I just bought a 1938 38/44 Heavy duty and the finish in the chambers and the gun is like a mirror. My 1989(?) 610 is downright rough by comparison.

I still come back to a simple view of the problem. If with the new technology you measure and find out the pressure is higher than you expected but the proof load still is with in the old pressure spec you are faced with a decision.

1) you can increase the new measurement spec so it matches with the older specification so the two techniques are "in sync". This places the emphasis on maintaining performance at the expense of a number.

2) you an reduce the old specification and download the new proof data so you maintain the new technology specification. This maintains the number at the expense of performance.

It appears to me that like most bureaucrats, the SAAMI protected the number at the expense of performance. Thus they down rated the loads. The politics behind the why is truly unknown, but I believe that the K frame guns had a lot to do with it.

Next the reloading manuals come along and their lawyers add in a bit more to a lot more "safety" to the load and you get to where we are to day.

Now you can stand behind the old mantra of "different guns, different conditions and different loads" old saw, but at the end of the day the loads are down relative to the old days.

So, I shoot a lot of 30's vintage 38/44's. Do I load them up with modern wimped out 38 special loads or pull out my 1930's to 1950's manuals and go for whole hog loads. Take a guess.




Remember Speer #8 first printing is your friend if you like the 38/44 loads! (although any Lyman/Ideal from #38 to #42 is a close follower)

 

[Clark]

SAAMI pressure derating over time

This is like the expanding universe appears to be moving faster the further away it is, judging by Doppler shift.

One alternate theory is "Tired Light". If the light goes far enough, maybe the frequency slows down.


So maybe those who register pressures at SAAMI are not nervous Nellie's, pantie waisted chickens, and cowards afraid of their own shadow. Maybe they are instead old men that are so weak they cannot get those standards up to the previous level. They are just giving us the senior discount.

 

[Lunie]

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.

There is a small amount of recoverable deformation even at very low pressures. As pressure increases, this elastic limit is exceeded, and the material is permanently deformed, but does not necessarily fail in the sense of coming apart. The coming apart happens when the ultimate tensile strength is exceeded.

I'm reasonably certain that most cartridges operate in the realm of plastic deformation, since we go through the trouble of resizing them. The material gets stressed beyond elastic limits, and after being fired, is slightly larger than it was before. I still think it is pretty neat that even after a material has been plastically deformed, there is still an amount of "recovery" after the force is removed. Just not enough recovery to return the material to it's pre-loaded dimensions.

 

[918v]

Right. The brass expands by .010" and then springs back .001" to allow the case to eject from the chamber.

What's also interesting is the deformation achieved by sizing and crimping. Many people fail to realize that brass springs back every time it is deformed, either by firing or by resizing.

Lead and copper also spring back, as do all metals. Lead springs back less than brass.