Manuals and Pressure Data

[steve4102]

Of all the Reloading manuals out there which ones actually have pressure testing equipment and which ones do not.

I know all the powder manufacturer's use real pressure testing equipment as they actually list pressures as does Lyman.

I know Lee does no testing as all, they just copy Powder Manufacture's data.

I also know that Sierra has no real pressure testing Equipment, but what about the others? What about Hornady, Speer and the rest that list actual firearms as their test medium? Are they like Sierra with no real testing equipment or do they have pressure testing equipment and just choose to not publish their pressure numbers?

Thanks
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[Shootest]

I think a good rule of thumb would be if a company makes assembled ammunition they must have equipment to develop loads and test it.

[Bart B.]

Ammo making companies may use SAAMI spec pressure and velocity barrels. Few, if any, rifle making companies' barrels are made to the same specs. This alone means a given load recipie will have different peak pressures in each type of test barrel. How much and in what direction is unknown unless you measure your barrel's internal dimensions then compare them to SAAMI test barrel specs. Typically, factory sporter barrels have larger bore, groove and chamber dimensions and they will produce lower velocities and pressure than SAAMI spec test barrels. Aftermarket custom match barrels may have smaller internal dimensions; they'll produce higher pressures and velocities for the same recipie.

Reloaders must realize that pressure levels listed with load data is only applicable for the specific barrel, component lot numbers and assembly techniques used to get the data. Their stuff will give different pressure levels for the same recipie with your stuff. How much and in what directions is unknown until valid pressure tests are made on your barrels. And if the pressure measuring system's not the same as what was used for the published load data, the numbers will be different. Visible indicators of pressure are the least reliable, accurate and repeatable of all systems.

There are places that'll measure your load's pressure in your firearm. Possibly H.P. White Laboratories, for one. Use RSI Pressure Trace software for a reasonable expectation. Or you can guess at what it is, cross your fingers then start shooting.

[steve4102]

Thanks Bart, but my question has to do with Handloading manuals and what type of testing equipment different companies use to acquire their data.

As I stated in my original post, Sierra has no testing equipment. They use regular firearms and they read pressures just like you and I do, they guess. To me this makes their manual less reliable then say Hodgdon that published data based on actual pressures.

What I would like to know is of all the companies publishing Reloading manuals which ones use pressure data and which ones guess.

[Bart B.]

The easiest and fastest way to get the best answer is contact the company then ask a competant employee what they use.

[steve4102]

The easiest and fastest way to get the best answer is contact the company then ask a competant employee what they use.

You are right, I could call, but I chose to send emails instead. I prefer their response in writing. So, far the only company that has returned my email has been Sierra and I have posted what they use.

[SL1]

The manuals that list pressures and velocities for guns that are NOT test barrels are actually giving "apples & oranges" data. The pressures are from the test barrel, while the velocities are from the stated gun. The idea is to provide handloaders with a realistic expectation of velocity for the loads listed. When the test barrel velocities are given, they are almost always higher than achieved in commercially produced guns you buy at a gunshop. (And, some companies probably don't want handloaders trying to duplicate the test barrel velocities in their own commercial guns.)

As for your question, I think that most manuals are now based on pressure-tested data. However, even some of those may contain a little old data that was NOT pressure-tested when you look at some of the older, out-of-favor cartridges like the .30 Herrett.

And, while companies like H.P. White will test your handloads for a fee, that testing is done in THEIR pressure barrels, NOT your gun. About the only way to get the pressure from your own gun is to use the Pressure Trace equipment. But, then there is the question of calibrating that equipment, so the numbers in your own gun will always be somewhat in question.

SL1

[steve4102]

You are spot on SL.

I just read Hornady #7 again. On page 74 they say that most of their data is developed in "special firearms designed to measure pressure". Then these "pressure tested" loads are fired in a commercial firearm for velocity.

They also say that not all data was acquired using test firearms. In some calibers and cartridges pressure barrels were not available, so they were tested in commercial firearms and inspected the brass case for signs of pressure, they guessed.

[F. Guffey]

Ammo manufacturers are not testing rifle actions, they are developing ammo, through a member on this forum I had the opportunity to purchase 100.000 test fired cases, a wild guess estimated 20% of the cases had a round test signature. I also had the chance to purchase all and or any part, the question was “ ‘would I have any concern with the round dents? Then there was another question: Would there be any information that could be gleaned from the test fired cases? My answer was “NO?”, I also said I would measure the cases for length from the shoulder back to head of the case “BECAUSE I AM ALWAYS LOOKING FOR CASES THAT HAVE BEEN FIRED IN TRASHY OLE CHAMBERS!” AND! I would measure the diameter of the cases at the extractor groove and case head.

I will never live long enough to use the cases I have, but I would have not hesitate to check the cases, size the cases and them load them up and fire them.

F. Guffey

[F. Guffey]

“I would have not hesitate to check the cases, size the cases and them load them up and fire them”

Like cases that have been fired in trashy old long generous machine gun clamberers, I would check the length of the chamber I was loading for first, I am the fan of transfers, I transfer the dimension of the chamber to the die, press and shell holder. I measure before, THEN! again after.

F. Guffey

[steve4102]

F. Guffey,
Huh?

[Unclenick]

Steve4102,

In other words, the manufacturers generally go for ammo safe in lowest common denominator guns (with the exceptions of "+P" and a few other specialty items). The load manuals use pressure and dimensional information compatible with manufactured ammunition in that regard. Mr. Guffey customizes his loading setup with reference to the individual gun's chamber(s) rather than to a manual's dimensional specifications. Getting an optimal relationship between case and chamber is one of the keys to maximizing performance and precision. Usually, though, it won't exactly match the load manual data any longer at that point.

Speer (owned by ATK) has their loads tested by Alliant (also owned by ATK), though they don't publish the pressures in their manual. Alliant publishes pressure for shotgun loads, but not metallic cartridges. Hodgdon publishes pressures for test barrels (click on the "Print" button at the Hodgdon Load Data site, and the length of the barrel and the case and primer used will appear in the header of the print preview screen).

The SAAMI pressure barrels have chambers made to SAAMI minimum chamber specifications, ±0.0005". The idea is that the tightest chamber will produce worst case maximum pressure. They also have standard pressure/velocity test barrel lengths. For rifle cartridges, most are 24" (though there are about half a dozen exceptions). So when you see Federal or Remington or some other commercial ammo maker list a velocity and no gun information, it is for the SAAMI standard test barrel.

If you want to read through the test methods and procedures, you can do it here. It's from 1992, and since then most companies have acquired graphical rather than simple peak detecting Piezo transducer measuring equipment as described in the document, but otherwise things are pretty much the same. There is also a more modern list of conformal Piezo transducer pressure values here.

As to measuring pressures, you can do that using the RSI Pressure Trace. It uses a fairly simple calculation of hoop stress from your barrel thickness over the part of the chamber you are gluing the strain gauge to. It's not directly calibrated except by gauge factor, but calculations by Denton Bramwell suggest it's rather better than you might suppose.

Below is something I've put up before that I took from data in that first SAAMI document I linked to. The upper table is the results of 9 different SAAMI spec copper crushers measuring the same lot of reference ammunition in different labs. Note the velocities are reasonably consistent, indicating actual pressure is reasonably consistent, but the measured peak pressures differ a lot more. CUP numbers are to be treated with suspicion. The modern Conformal Piezo transducers (lower table for 7 facilities measuring a different reference round), with error less than half what the copper crushers can produce. But understanding this limited level of precision goes a long way toward explaining why even load manuals with pressure measurements can disagree about maximum loads, sometimes significantly, and why you occasionally hear of a manual load that causes pressure signs in a user's gun, despite reported pressure measurements suggesting it's safe. The strain gauge system can keep up with the Piezo absolute accuracy levels shown in the tables and better the copper crusher consistency pretty easily.



The SAAMI system, when you look at it in detail, actually includes quite a bit of wiggle room for error. For example, a .308 Winchester maximum average pressure (MAP) is the average of the peak values for a 10 round sample taken when the ammunition is newly loaded. That average is allowed to go up to 66,000 psi for a 10 round sample pulled at any future time as the lot ages (maximum probable sample mean, or MPSM). The Maximum Extreme Variation (MEV) is the pressure a worst case individual round is allowed to reach, and for .308 Winchester the MEV is ±12,800 psi. So the maximum pressure for a new non-proof round will be:

62,000 psi + 12,800 psi = 74,800 psi.

That's not quite up to proof pressure (82,000-92,000 psi for .308 Win), but you can see how much wiggle room there is. In a .308 Win firing Varget under the 175 grain SMK, QuickLOAD says that would take a charge error about 5.8% too high to reach the upper side MEV, which is over 2 grains of powder. I know some handloader's powder measures are a little irregular with stick powders, but not that irregular.

Anyway, there's a good deal more uncertainty and wiggle room in pressure numbers than most folks realize.

[steve4102]

Thanks Nick, but do you know of anyone other than Sierra that publishes loading manuals without pressure testing equipment?

[Unclenick]

Sure. Almost all old manuals were done without pressure test gear. Lyman loads that don't list pressures were done without it. These are the loads that list a production firearm instead of a Universal Receiver (used for SAAMI test barrels). My Hornady manual (#6) appears to have been done without pressure test gear, as they list standard test firearms, like Sierra does. So does Speer, btw, but Speer says theirs are subsequently tested by Alliant (probably for insurance reasons). Nosler uses special machine rest guns they get barrels made for by various custom barrel makers. Whether they've fitted these with strain gauges or other pressure test gear, they don't say, but they certainly don't report any pressures (at least, they didn't in the Nosler Reloading Guide #6). You also find a few (especially pistol) loads that show a production gun's name in the Nosler manual.

[pathdoc]

And then there is the confusion that some load manuals start their charge weights for a given calibre and ANY bullet of a particular weight where some specific projectile manufacturers (I'm looking at YOU, Hornady!!!) tell you to stop.

Pick one, decide to trust it (I elected to trust the powder manufacturers first and foremost), start at minimum listed and watch carefully for pressure signs. And make notes of what you did before you pull the trigger. No, they have no obligation to compensate you under law (as all the reloading guides - paper and online - state over and over), but if you can demonstrate you followed their instructions, they can at least start to look into what happened to you and maybe identify lot-number issues and stop the same thing happening to someone else.

I do not load to maximum, and aside from one excursion to within a grain to see what would happen, I never will. (For the record, accuracy started to suffer long before pressure signs appeared, so I backed off and didn't bother going there again. My rifle liked minimum loads and that was fine by me.)

[Clark]

I think that actual pressure is a red herring, unless one is selling ammo or writing load manuals.

I work up in my strong rifles until the primer pocket gets loose, and then back off a safety margin.
The hardest thing for me is calculating the magnitude of the safety margin. Vernon Speer wrote 6% for making manuals in 1956. Along with the other variables to consider, I have to include the temperature effects on the powder and the range of temperatures my chamber might be.
So I was grateful when Hodgdon came out with the extreme powder series.
Kombayotch replicated the temperature coefficients.
Then Aliant came out with AR Comp.
Kombayotch replicated that AR Comp is even flatter.

Last year I drove 900 miles to load, target practice, and shoot deer. I had built a wildcat rifle, a 257 Roberts Ackley Improved Rimmed. I had necked down and turned the necks on Norma 7x57mm Rimmed brass. If normal brass should go to 67kpsi in Quickload, then the rimmed should go to 80kpsi. Wrong. The brass was soft and giving up the primer pocket at 62 kpsi in Quickload. I had to switch from H4895 to H4350 and back off from 62kpsi. It did not matter what the numerical value of pressure actually was, what mattered was the effects of pressure. I had to back off from the loose primer pocket effect.

[F. Guffey]

And then there is full length sizing as in they full length size everything, the part I do not get is the part where “they do it therefore so should we”. I built a wildcat, I formed cases, not a problem but I did not have the dies so I was forced to use several dies, when finished I went to the range to finish forming the cases. And, I was told I was going to blow the gun up. Because I was not ignorant I did not say “HUH!”, but according to my cakel-later with time added as a factor I was safe.

After the cases were formed the bullet and powder charge I used to form the cases was at or beyond maximum load. One of the individuals that said “In my opinion you doing some risky stuff” caused me to verify what I was doing was a safe plan, I Called Hodgdon. Seaweed, my friend from Arizona, expressed concern and went to the trouble to send drawings, then he looked at the drawings, at which time he said there were details in the drawings that he had never noticed before.

F. Guffey

[steve4102]

Because I was not ignorant I did not say “HUH!”

Huh? Because your post has nothing to do with the Original Question.

Of all the Reloading manuals out there which ones actually have pressure testing equipment and which ones do not.

Not sure who the Ignorant one is here?

[F. Guffey]

Steve, I was asked if I had any interest in the test fired cases, my answer was "no", but! if someone would allow me to set up on the line and measure the cases before and again after firing I would have an interest. I was informed that was not going to happen. That leaves purchasing new factory ammo, measure before and again after. All of my life to get pressure result I have been of the opinion there has to be something in and or near or on the chamber, the case is in the chamber when fired, the case has a flash hole, I have a flash hole gage, the case has a primer pocket, I have endless ways to measure the primer pocket, then there is the case head thickness and diameter, there is an extractor groove, measuring the diameter of the case at the bottom of the extractor groove is doable, and I have shell holders that do that also.

I have cases that I have fired to test receivers, I was informed 5 receivers I purchased were suspect. One firing, that was all that was required to render the cases scrap. flash hole, primer pocket, case head, extractor groove diameter, not one part of the test cases escaped the effect of the test. There is always the question "What are the first signs of pressure?" Number one answer, 'primers'.

The 5 receivers were not suspect, but, if I continued to test the receivers failure was sure to come.

F. Guffey

[old roper]

steve4102, If you look at the picture of Sierra underground shooting tunnel http://www.sierrabullets.com/about-us/sierra-story/ on both side you see a set of Oehler Ballistic Screens.

We got a quick tour of the tunnel and ask about pressure testing and was told all that is send out. They had break between testing for the 6.5x47 Laupa so didn't get to look down the tunnel but they were using a Hart barrel machine rest,Redding dies and press.

[F. Guffey]

And then, there is the narrow window. The narrow window between minimum ‘starting’ and maximum load. It could be said an extreme spread would be 5 grains, pistols are more critical. Then there is the difference between neck sizing and full length sizing.

F. Guffey

[steve4102]

Then there is the difference between neck sizing and full length sizing.

What difference would this make.

Are you suggesting that neck sized brass has more case capacity then FL sized brass? If so, I disagree.

As soon as the primer ignites the powder the cases, both neck sized and FL sized, expand to fit the chamber. This happens before the bullet exits the case and before peak pressure is achieved. It reality the neck sized case and the FL sized case will have the same capacity once the round is fired.

[F. Guffey]

and I was asked if the little round dent in the side of the case body would bother me? I said “no”, the dent on the side of the case would allow for one more way to sort cases.

F. Guffey

[Bart B.]

Steve, a few folks have made muzzle velocity tests with the same recipie in both full length and neck only sized cases. They report a small, 10 to 15 fps difference in average velocity between the two. Their reasoning is the powder charge has a different volume at its start up of the burning process and that effects the pressure curve's shape and magnitude.

Personally, I don't think it makes any significant difference. Wouldn't matter to me if it did.

[steve4102]

Steve, a few folks have made muzzle velocity tests with the same recipie in both full length and neck only sized cases. They report a small, 10 to 15 fps difference in average velocity between the two. Their reasoning is the powder charge has a different volume at its start up of the burning process and that effects the pressure curve's shape and magnitude.

Naw, 10-15fps is statistically insignificant, you know that.