Explain this load data...

[Galil5.56]

Looking over data booklets I have had for decades, I always love to see how max charge weights go up and down over time using the same components.

Yes, what was considered max may have changed, and CUP vs PSI is a factor, but when I find a very drastic difference that can not be explained, I wonder what is going on. A very glaring example.

My circa 1995 Hercules booklet lists a 125 grain FMC load using Unique, as does my 1996 Alliant booklet that was the first from Alliant, and the current Alliant website also lists a 125 grain FMC/Unique load as well. All sources list OAL as 1.15", barrel length 4", and WW small pistol primers. Now here is where it gets interesting. Although we do not know the exact diameter or type of FMC bullet used, we do know its weight, and the listed max charges for Unique are listed with their corresponding pressure in psi as follows:

1995: 6.2 grains 1170 fps 31,300 psi
1996: Same
2007: 4.9 grains 1077 fps 31,745 psi

Hmmm, Alliant tells me that Unique has the exact same performance spec as it ever has (even the "improved" version) when I asked about this data anomaly, and from tests I have seen comparing the two this would seem accurate. Yet when comparing psi-to-psi using identical components, and only the charge weight changes, 1.3 grains less of Unique in today's world has higher pressure??? This is a very substantial charge weight difference that lot-to-lot variation can not come close to explaining. The velocity drop looks very plausible, but the increased pressure???

I asked them if it was possible that the propellant they used for this Unique data may have actually been drawn from a recalled batch where Bullseye was accidentally put in the 8 lb drum instead of Unique, but was told no, and that the data is accurate??? Other than a CYA for legal reasons, what do you think could explain the data?

 

[JesseL]

There are a ridiculous number of variables (beyond what's listed in the load data) that will affect pressure and velocity. Add the variations that appear between different pressure testing apparatus, and I'm not surprised by the discrepancies you're seeing.

I'd just chalk it up to the whims of the interior ballistics gods, and consider this a reminder of why they recommend working up slowly from the starting loads.

 

[rcmodel]

Between 1995 and 2007 they may have switched from a copper-crusher pressure gun to a PIEZOELECTRIC TRANSDUCER test method.

That would allow them to see pressure spikes that were not seen with the old copper-crusher method.
All it could measure was maximum average chamber pressure.

The new method shows on a computer or oscilloscope screen with the pressure curve shown as a graph over time.
It has opened a lot of eyes on what is really going on inside the chamber, and some revised loads being printed in recent years.


rcmodel

 

[ReloaderFred]

I agree with rcmodel, the testing equipment has gotten better, and combined with computers, they're getting the overall picture of what's happening, rather than just a snapshot.

Hope this helps.

Fred

 

[Galil5.56]

RC Quote:

"Between 1995 and 2007 they may have switched from a copper-crusher pressure gun to a PIEZOELECTRIC TRANSDUCER test method.

That would allow them to see pressure spikes that were not seen with the old copper-crusher method.
All it could measure was maximum average chamber pressure."

The exact reason why I did not include any comparable data from my very early 80's Hercules data showing pressure done in C.U.P. I wanted to keep likes with likes. I understand and accept some variance/tolerance with data, but to have a rise in pressure using more than 20% less propellant and otherwise identical components, test conditions, ect, seems like to me either the wrong/bad propellant was used, there was a misprint, or something else is being done.

When I was at a job interview with Accurate Arms Powder while they were still in TN, I asked a lot of questions when we hit the ballistics lab, and one was about propellant speed tolerance. I was told they go for a 3% +/- of spec. Also inquired about test conditions, (i.e temp), got a quick demo of their test barrels, pressure testing gear (pretty sure it was Piezo) etc... This was in 1992, and I can't help but think that Alliant had far better lab gear than Accurate, and equal if not superior tolerance specs in 1995/96.

Thanks for the replies, and sharing your thoughts.

 

[CZ57]

Maybe the simple solution is that ballisticians come and go, also. Powder manufacturer pressure data is useful, but I've never found it as reliable as what you'll find in a Lyman manual. Consider that Alliant is only giving you their max. charge, then telling you to reduce by 10%. More reliable data would take you nearer to the actual max and stop 1000 - 1500 PSI short to allow a margin of safety.

The Piezo system was around long before 1995. In fact, when laboratory tests have been conducted, the Piezo system has not proven to be more reliable than the Crusher method, just more convenient. Funny that many companies are going back to the CUP system. Particularly for magnum revolver and high pressure auto cartridge loads. More reasons to own a Lyman manual.

The Piezoelectric transducer can be more readily used in conjunction with diagnostic test equipment, i.e. computer. So, who are the gods? Were they even reloaders before they became ballisticians? In most cases they are now, but their engineering degree/license was the prime motive for their hiring.

I talked to Johan Loubser at Accurate/Ramshot a few years ago and he informed me that there could be a move in the future to the Piezo method used by the Europeans: CIP. The values are much more similar to results from the CUP system.

I've seen the gods, and they are us. Provided we have the diagnostic tools and the ability to use them. We have a good many reloaders here that have as much or more practical experience; very few of us have the tools. The folks at Lyman are reloaders as well as engineers. There is no degree or license that I'm aware of for a ballistic engineer in the US. There is definitely a CYA element here. That is the reality of a society obsessed with liability litigation. CYA is a means to counter the obsession. Looks like you're describing a 9 X 19mm load. The SAAMI Maximum Average Pressure for the 9 X 19mm is 35,000 PSI/33,000 CUP. Both loads are under 32,000 PSI.

There are variables, and as JesseL pointed out, this is why we work up from start charges: to observe the variables. Unfortunately, one of the biggest variables is SAAMI ambiguity. For a very small percentage of reloaders that do experiment beyond reasonable maximums, SAAMI has chosen to punish all of us: BootCamp discipline. And, the ambiguity is why some of these "hot rodders" exceed the accepted maximums. They assume that the data is overly conservative, making this a case of, "which came first, the chicken or the egg?"

If you don't have a Lyman 48th Edition, or the Pistol & Revolver III, I recommend you add it to your reloading library.

 

[Bullet]

Galil.556
You said they used 4 inch barrels for their testing. But not necessarily the same barrel. I’ve noticed different velocities in my gun from the reloading data. Maybe the difference is the barrel used in the testing plus different bullets (even if the same weight).

 

[Ol` Joe]

The accuracy of the system used can also be a factore in differing pressure claims. There was a artical in Varmite hunter magazine once on the various methods of determing pressure and their accuracy by Denton Bramwell.
He found the copper crusher system to be accurate to ~ 1800 psi if I remember and a strain gage system to ~ 650 psi. These are from memory so they may not be exact, but I believe I`m within a couple hundred psi or less. If the older load was measured by crusher the psi could be over 33K psi or under 30K psi. The later pressure on piezo equipment is likely within 31-32K psi and much more reliable as true.

 

[CZ57]

Joe, you might want to revisit that article. First off, the Crusher tests would have given pressure in Copper Units of Pressure; not PSI. If values for loads were compared, the PSI measurement would run higher than CUP. If a strain gauge produced more accurate readings than Crusher or Piezoelectric transducer, the ammomakers would be testing with a strain gauge rather than Crusher or Piezoelectric.

 

[Shoney]

Pressure, whether derived from testing PSI, CUP, LUP and/or physical signs of the pressure on the brass, is how the manuals determine their minimum and maximum loads. All load manuals have data well under the SAAMI pressure specs (lawyer driven data). Combinations of factors can cause great variances in pressure. JesseL talked about a ridiculous number of variables. Here are a few factors:

Primer: strength, brisance - is a measure of the rapidity with which an explosive develops its maximum pressure
Barrel: length; tightness of chamber; tightness of bore; height of the lands, or no lands if polygonal; distance of bullet to lands; temperature of barrel;
Bullet: diameter; bearing surface of bullet, alloy of bullet; shape of bullet; crimp; seating depth/OAL (affects cartridge volume);
Brass: new/used; elasticity; manufacturer, wall thickness; volume;
Powder: new, aged, old, batch powder was from;
Weather: ambient air temp., barometric pressure, humidity; elevation above sea level
Other: I am sure I have not listed all

Now, mix and match them. Anyone care to calculate the number of possible combinations?

 

[Ol` Joe]

Joe, you might want to revisit that article. First off, the Crusher tests would have given pressure in Copper Units of Pressure; not PSI.

CZ here is a copy of the artical, the error figures are on pg 7 toward the bottom.
http://www.shootingsoftware.com/ftp/dbramwell july 19 04.pdf

BTW ammo makers are useing strain or Piezo today in place of crusher methods. Speer, Nosler, and other component makers are also switching.

 

[ArchAngelCD]

Or maybe they are lowering the charges to make the lawyers happy and lying to us about the pressures. It seems hard to believe a 20% decrease in powder will yield the same pressures even with the newer testing equipment. I'm saying that because back when they listed the higher charges there were no pressure problems and the guns weren't blowing up. 20% over Max is very big and would have done damage but never did. That leads me to believe they are now lying just to make sure nobody litigates.

We are being cheated because we are not getting the full potential from our reloads. It's just not right we have to put up with anemic loads and load data. Years ago there was load data for "hot" .38 Special rounds using lead bullets that they now call +P. Under the +P data sections there is no data for lead bullets. They want to protect us from leading the barrel but who asked them? I wrote Hodgdon and asked them for .38 Special +P data using Longshot powder and lead bullets. They wrote back telling me they didn't get good results with Longshoit and lead bullets yet they have Longshot and lead bullet data for the 9mm. That makes no sense at all. There are many more examples but I'm sure everyone has seen them for themselves. It's just not right we are being denied the data that would allow us to get the most from our chosen calibers but that's seems to be the normal now. It's just no right...

 

[DWARREN123]

Different ways of measuring pressure and possibly reformulated powders.

 

[CZ57]

The change from Crusher to Piezo occurred quite a few years back. The current trend is that companies are once again furnishing near original pressure data for magnum revolvers, and are using the Crusher and Copper Units of Pressure. Check current Accurate data, or the Lyman P&R III.

I went to the link, Joe. Thanks, it's interesting hypothesis; possibly geared toward selling a product and a single case example. Look at page one under the heading of History, second paragraph.

 

[joneb]

I'd just chalk it up to the whims of the interior ballistics gods, and consider this a reminder of why they recommend working up slowly from the starting loads.

? what about H110, Hodgdon lists 16.7gr for a 158gr XTP w/ Win. case and WSPM primer and 10" test barrel, and warns not to reduced by more than 3%. And then I have Hornady data that list a min of 14.1 and a max of 15.8 of H110 w/ the 158gr XTP w/ hornady cases and Fed 200 primers from a S&W M27 8 3/8" barrel.
How would you determine a start load ? I don't have a M27or a 10" barrel