Speer # 13 & 14 Reloading Manuals---

[Unclenick]

Clark,

You're not the first born nerd engineer. That would have been one of my professors at school 40 years ago.

I think you'll find your extractor groove expansion has the same relative accuracy as case head expansion. Good article here on it. As you might imagine, if even two different copper crushers with calibrated slugs cannot agree on what pressure a load has, an uncalibrated piece of case brass does somewhat less well.

Buying a Pressure Trace and calibrating it with commercial reference loads is about as close as you'll get. If you are careful about it.


SL1,

I can't say I see that 10% burning rate margin with any consistency. I think there's a problem with some of the powder data coming from lab analysis of different lots. Try loading some magnum pistol rounds in QuickLOAD using H110, then swap in the 296 model. Indeed, take a look at all the parameters for those two powders. Since they are actually the same St. Marks powder, it makes one wonder how consistent the makers really are able to keep their controls, since the parameters were apparently measured in Hartmut's lab?

In another thread a rather vehement board member said Federal now uses Reloader 15 in federal GM .308 Match, and used to use IMR4064. I have some of that older ammunition and had pulled bullets and found a longish stick powder (like IMR4084) slightly compressed with an average charge weight of 43.5 grains. In QuickLOAD I used a 56.9 grain water capacity case (my old Federal cases were that size out of a very tight match chamber) and put 43.5 grains of IMR4064 under the 168 grain Sierra MK at 2.8" COL and "fired" it in the program through a 24 inch barrel (test barrel length). The predicted velocity was right on 2650 fps. Federal's data claims exactly 2650 fps from a 24" test barrel for that load on their web site.

So, some of QuickLOAD predictions seem awfully tight. At other times not so much, though the throats and other matters certainly can affect that rather dramatically. Lever guns with high pressure loads can be especially problematic, since they often stretch their frames during firing, then size the case back down as the steel returns to shape, so you can't get an actual case volume at peak pressure. The program also seems to have some result anomalies modeling digressive burning (note how long a pistol barrel you have to use with target loads to burn Bullseye 100%). Compressed load pressures tend to be under-predicted with some powders.

One factor most people don't bother to adjust is the cross-sectional bore area and that can move things around a few feet per second. Same with the weighing factor. Also, the barrel friction calculator for very long barrels turns out to improve calculations for short barrels, too, in some instances. It is worth turning on to double-check the what you are running?

[Clark]

I wanted to point out the assumption that load books are a real reference, with humor.

[Clark]

Denton Bramwell, the man who can be taught processes, but cannot reason.
I have spent too much time trading flames with him.
He just does not get it, and is stuck fearing pressure.

[SL1]

Unclennick,

I think we are saying the same thing about QuickLOAD. I can match some data pretty well, both the data from books and from my loading records. But, other data I have not yet figured out how to match. I can always FORCE a match to just velocities, but I can do it severeal ways that give different pressures. So, I don't know which, if any of those ways are giving the real pressure. As we have both pointed-out, you can get some really different veloctities and pressures by switching between powers in QuickLOAD that are supposed to be the "same." Swithching WW-296 and H-110 is not so significant as switching some others, such as ADI-AR-2207 and H-4198. And, pressure-test data in some manuals that show both WW-296 and H-110 also say that they are not identical, though close. From what I have been able to tell from the little velocity + pressure data that I have seen, those differences are more likely due to actual pressure differences due to different lots of the "same" powders than they are to random errors in the pressure measurements at the ballistic labs. So, I think that same explanation applies to the different lots used by different labs in doing their pressure testing as well as to the different lots we use when we work-up our own loads. And, of course the guns make a difference.

So, I was not trying to trash QuickLOAD, but I was trying to squash Clark's apparent advice to this forum that pressure-test results in reloading manuals were not as "good" as the results from QuickLOAD and you could just dispense with the data and use the program. As you know, even the program itself has a warning to that effect in a permanent yellow band across the top of the screen.

SL1

[Clark]

CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assume any liability for any damage or injury resulting from use of this information.

Johnny Guest wrote this caution for my posts, many years ago, for TFL and THR.

When I shoot double loads in 9mm, Quickload says that it is over 1 million psi, but the primer does not pierce and the case does not bulge.
Hartmut Broemel, the author of Quickload, is the first to admit, the QL model breaks down when a straight wall case is overloaded and blows out a fireball.

But I have many bottle necked cartridges that I have loaded [remember how many cartridges I load?], gone to the range, shot a string, wrote down the velocity, and the the prediction is in the middle of the string.

When you can do that in 308, 8x57, 260R, 257RAI, 7mmRM, etc, then you know you have got the program dialed in.
For bulk powder, instead of canister powder, QL is often better off with a substitute identity powder. I got 32 pounds of surplus bulk IMR4895, that the QL model for H322 is right on the money for pressure and velocity, and good enough on density.

I am not saying that beginners should not use load books.
The cook books are fine for them.

I am not saying the beginners should not read Denton Bramwell.
I have my CEA-O6-250UW-350 strain gauges right here, and I have designed and built instrumentation amplifiers for them.

What I am saying is that the pressure does not matter, the effects of pressure do. Pressure is a handy abstraction, but those who read Speer 13 will get many red herrings from bogus data in trying to divine the causes of pressure.

I wrote the long humor essay in reaction to the errors in Speer 12 and Speer 13. The recipes in that cookbook have little to do with accurate data.

There should be a warning in Speer load books; "We made up these loads and a committee altered them. But we are pretty sure they are safely between a stuck bullet [too wimpy] and a failed case [too hot]. These load are not to be taken seriously as data by scientists and engineers."

I felt like such a fool for having read the data and tried to make sense of it.
Much like watching Ice road truckers before realizing the trucks are empty and the lines are scripted.

[SL1]

Clark,

You keep making the flat assertion that Speer data is "made-up" and incorrect. But, you don't say what data and logic support that statement. If you want us to take you seriously, you will need to explain what data you have and what logic you use to prove that Speer data is not proper in some way.

SL1

[Clark]

If we plot this history of Speer 44 mag loads, we will see a triple humped camel.

"Speer 3" 1959 44 mag 240 gr. JSP..........23.0 gr. 2400 1564 fps
"Speer 6" 1964 44 mag 240 gr. JSP..........23.0 gr. 2400 1564 fps
"Speer 7" 1966 44 mag 240 gr. JSP..........23.0 gr. 2400 1564 fps
"Speer 8" 1970 44 mag 240 gr. JSP..........23.0 gr. 2400 1521 fps
"Speer 9" 1974 44 mag 240 gr. JSP..........19.5 gr. 2400 1344 fps
"Speer 10" 1979 44 mag 240 gr. JSP&MSP 22.2 gr. 2400 1392 fps.
"Speer 11" 1987 44 mag 240 gr. JSP&MSP 22.2 gr. 2400 1452 fps
"Speer 12" 1994 44 mag 240 gr. JSP&MSP 17.7 gr. 2400 1271 fps
"Speer 13" 1998 44 mag 240 gr. JSP&MSP 21.0 gr. 2400 1434 fps
"Speer 14" 2007 44 mag 240 gr. JSP&MSP 21.0 gr. 2400 ???? fps

[Unclenick]

Not to put words in your mouth, Clark, but without rereading it, I think your earlier post said you noticed the starting load and mid-load ratios were the same but that the velocities associated with them don't track in QuickLOAD, but do track with a pressure formula given in the manual? Therefore, the lower loads were not measured, but based on using the top loads as arguments for that equation. Then you also suggests the top loads were derived from other sources, and that idea is based on having stared at the other sources long enough to see the relationship? I'll have to try that. The only thing against Speer manuals I've ever heard is that the earlier ones have some very hot load data in them, so, presumably, those earlier books were not derivations, but rather were loads Vernon Speer worked up in real guns.

I have to point out, however, that in working on pressures for compressed loads in the .280 Remington, I have also had QuickLOAD fail to track. This was with a 160 grain Sierra bullet and IMR4831. Uncompressed, with a 5% reduction in the burn rate as an adjustment, it tracks Sierra's published data for the combination (which is actual fired data, by the way; I spoke to the technician who did the re-firing for the most recent version, which he said took him a year to do) within 7 fps. Very tight. The .280 owner I was looking at number for is running faster than QuickLOAD predictions with his compressed loads, which go beyond the Sierra manual recommendations. QuickLOAD tracked well enough at his starting load, but he got significantly higher-than-predicted velocities as he compressed it further. In some instances I wound up shrinking his measured fired case volume until the compressed percentage was at about the square of the actual compressed percentage of the fireformed capacity before the velocity caught up. Needless to say, that shows some pretty high pressures. Not enough to burst a modern gun, but well into the proof load range with his highest values.

That kind of unexpected performance varies with the powder, as it does in real life. Dave Milosovich published a comparison of the amount of IMR4895 and IMR4064 it took to reach some fixed velocities in a .308 Match rifle (24" tube), showing how the apparent burning rate ranking of the two reverses position as the load gets warmer.

Vel. fps   2200      2300      2400      2500
IMR4895   37.0 gr   38.5 gr   40.0 gr   41.5 gr
IMR4064   35.9 gr   38.0 gr   40.1 gr   42.4 gr

I've gone through the argument before about the computer verses the manual, and I think they both have their uses as long as you stay aware of their limitations. Those manuals using actual fired data are firing it in real guns, which is a good general reality check, but they still aren't your particular gun, so it isn't necessarily tracking your performance well. The computer can be made to match your gun perfectly, but it's a virtual gun and not a real firing. I like the data that was fired in pressure guns from the standpoint that the chamber is SAAMI minimum, so it should be worst case for peak pressure. The downside is where those guns are still the old copper crusher guns rather than the modern Piezo transducer guns.

Somewhere in the second half of the 90's, it seems to me, Precision Shooting had some reporting about how poorly a given load's pressure testing matches from one copper crusher to the next, to the point, it was argued, that even allowing that CUP doesn't match absolute pressure well, the whole technology is not replicable enough to form the basis of a solid metrology method. If you get the same exact copper crusher, operated by the same exact technician, using the same lot of calibrated copper slugs, though, you do seem to be able to repeat results well enough to determine whether the pressure of one load matches the next or not?

I think that probably brings us to the main point I take away from Bramwell's analysis, which is simply that those persons who think a couple ten thousandths of case head expansion on a sample of just one case means they are seeing a peak pressure of 60,000 psi are just kidding themselves. It was anywhere from 35,000 to 70,000 psi in Bramwell's one set of data for 95% confidence, with cases that had identical history. What Bramwell failed to mention is that if you calibrate a particular lot of weight-matched cases and fire about thirty rounds at each load level, you actually will accumulate enough data that the mean diameter of the thirty is a pretty fair pressure measure. Most people just don't want to shoot that many rounds of any one load. Also, work hardening will see to it that the calibration changes with each reloading cycle, so it all has to be done with brass that has the same load history. Frankly, if you want to know pressure, you really are better off buying or, in our nerd electronics engineer's case, making your own strain gauge pressure instrument.

Would you want to know the absolute pressure, anyway? Well, you might. It could be for the same Reason SAAMI does: so you know your ammo is compatible with other rifles with the same chambering. But you will still need factory reference loads to get your gun's peculiarities taken into account in the measurement. Match shooting has been known to involve backups and loaners from time to time. Hunters borrow each others gear frequently, too, so you wouldn't want an ammo mix-up there to cause damage. As a service rifle match shooter, my main interest is in keeping the ammo in a pressure range that won't bend op-rods or otherwise screw up the gas operating system. The danger of bursting the gun is nowhere on the horizon in the mechanism-safe pressure realm, so that really doesn't enter into it for me working loads up in those guns. Finally, I think the extreme longevity of service rifle receivers and bolts proves service load pressures don't introduce significant long-term fatigue in these weapons. So, even for the bolt service rifle guns, I like to stay in that range just to be sure to continue that longevity.

That said, you may not care about any of those things. A single gun to which the ammo is dedicated, is its own peculiar self. Most modern guns will handle rather higher pressures than their cartridges are rated for. Hatcher tells of running destructive tests in which he could not blow up the properly heat treated receivers he was testing because the ammo's case heads always blew out first, damaging just the bolt face and stock and magazine. So, he had the arsenal imprint the head stamp extra deeply into some cases for him. That additional work hardening was enough to let him load those cases to blow the guns up. He may have been using blank powder to do it? I've forgotten? I don't think he could fit enough IMR powder in to do the job.

So, is there a hazard in relying on case head expansion or even extractor groove expansion to tell you that your load is safe for a particular lot of brass? A lot of brand-name brass is now made on contract by overseas manufacturers, so I think it is possible to get extra hard heads. I know there have been extra soft ones. Even if you got a case head hard enough that it would not expand at all before you reached fatal pressure levels, the bolt would be sticking or other pressure signs would most likely occur well in advance of that, thus warning you off further charge increases. Fatigue is another matter, though, and short of periodic, very precise dimensional measurements to prove the steel is staying inside the 100% elastic region of its strain curve, you're not going to see it coming before a lug cracks or your headspace grows.

The guys who argue CHE is a good indicator because it reflects what is happening to the steel would also be wrong. Normally, the case only expands to touch the steel at the breech face, not normal to the bore axis as the pressure ring and the case forward of the pressure ring does. The case head and extractor groove normally have air space around them, leaving their diameter to be upset indirectly by being driven into the breech. So you really end up just measuring what the pressure effect on the brass itself is, and nothing else. Whether you are at pressures and temperatures that will tear up your throat or cause the aforementioned fatigue over time, you don't know from that indicator. It just tells you about that lot of brass.

As an aside on soft brass, Federal rifle brass is known for being soft and Dan Newberry states flat out that he does not consider Federal rifle brass suitable for reloading. John Feamster wrote about using it in the Precision Shooting Reloading Guide, and found that with normal (both as to gas gun charge weight and velocity) loads, he only got about half the life from it that he did from most other brass before the primer pockets got loose. That's an example of soft heads that would indicate maximum pressure at sub-par performance levels for the chambering and for many rifles. Just thought I'd toss that in as a reverse example.

[Clark]

Uncle Nick,
If I wrote anything as well as you, I would include an invoice, so I would get paid

I think that Glenn Rice, an EE, is the one who normally debates Bramwell about PRE and CHE, an EE, and I , another EE, just don't have the stomach for it. My cousin from Sweden who worked at Norma, another EE, can do internal ballistics calculations. My father, another EE, has dozens of gun patents, and was chief engineer of a fortune 500 company for 40 years.

Don't expect any of that greatness from me.

I have simply realized that the primer pocket in the Large Boxer primed 1889 7.65x53mm case head is the weak link. When primer pockets are loose, I throw the brass away. I would like long brass life. The game then becomes how much velocity I can get, and still get long brass life.

Many others have figured this out.

In communist propaganda confuses the zero sum gain of sharing in a family with the non zero sum gain of a free economy. The instinct to not be cheated is exploited to advance a collectivist agenda over an individualist one.
There is a book, "How the mind works" that shows some logic problems, and demonstrates that people are much more logical and thorough thinkers, when they suspect that they are being cheated:
http://www.amazon.com/How-Mind-Works.../dp/0393318486
Likewise Bramwell confuses commercial ammunition constraints of a standardized average max pressure with the long brass life constraint of personal handloads. The preservation instinctive fear of exploding guns is exploited to advance a pressure measuring debacle over a brass management system. Denton is afraid to work up loads to the brass limit, is sincere, and could probably pass a lie detector test about what he sells.

I have done some experiments with AA#5 and Power Pistol that suggest the burning rate vs pressure curves have different shapes.
In a work up, the AA#5 is quick to go from no pressure sign to bulging cases, blowing holes in cases, splitting case heads, piercing primers, splitting chambers, and lots of secondary failures resulting. While Power Pistol seems to climb is pressure slowly, making a bigger and bigger fireball out the muzzle.

I have done work ups with rifles to see what happens, and I am sad to say 3 Mausers had unscheduled disassemblies this year.
Working up to the practical limit of brass change and reducing the load by 6% ala Vernon Speer 1956, may be a goal, but what to measure?
I do not like looking for primer pocket looseness directly:
1) The primers do not reliably fall out.
2) The primer pockets do not expand symmetrically and so cannot be detected with round pin gauges.
3) Feeling primer insertion force is subjective and not convenient at the range.
4) Primer pocket growth is cumulative.

So I measure the extractor groove before and after firing. I spin the case in the dial caliper jaws, while looking for a peak. New brass has a symmetrical outside diameter at the extractor. The threshold of short brass life will likely be an asymmetrical expansion.

I don't know if there are a million guys doing that, or if I am the only one.
It is not PRE or CHE.

[brickeyee]

I have 5 different books to choose from.

Only 5?

I have at least 8 feet of shelf full of loading books.

OK great.....still it's not the same as firing from a REAL firearm.

And they often use minimum chambers also, further increasing pressures.

The loads need to be safe in ANY gun of that caliber (unless they mark the data like .45-70 is divided into classes based on action strength).
Last I checked bolt, lever, or auto had nothing to do with what pressure any particular load will develop, though different pressures and even curves may perform better or worse in various action types.

You can alter the powder burning rates in Quickload to make it match different lots of powder.
The methods are out there, but require some decent knowledge of what and how much to change the parameters.

[SL1]

Looking at Clarks post with the Speer data from manual to manual doesn't seem to prove anything. Yes, the loads changed a few times in about 50 years, but so did:

models of guns used to give velocities (which are NOT the SAAMI test barrels)
wear on the guns used to give velocities
powder lots
bullet construction
bullet seating depth
pressure test equipment
case lots
primer lots

In the #14 manual, they have a comparison of 3 different .357 magnum loads shot through 30 test guns and a pressure barrel. There are HUGE differences. Looking just at the 9 revolvers that all had 6" barrels, the loads varied by 376, 275, and 282 fps for 125, 140 and 158 grain bullets, respectively.

So, it doesn't surprise me any that the velocities will vary between manuals when they reshoot the velocities from a differnt gun with different powder, etc. That is part of the problem with reporting velocities from a commercially available gun instead of the SAAMI spec test barrel. But, it still seems better to me that they do that, because the velocities from the test barrel are unrealistically high for revolver cartridges for a lot of reasons, including: no cylinder gap, longer barrel, tighter chamber. I just wish they would report BOTH velocities so that we have some idea how to model these things now that the tools are becoming available to us. Reporting case volumes would also be nice.

Clark's posts mainly discuss using case head expansion measurements to control loads for very strong rifle actions, but he used a revolver cartridge for his example of Speer's unworthiness. Case head expanson is not a good tool for most revovlers, because the revolver can fail before the case. That is especially true of the older, lower pressure cartridges.

I have used pressure ring expansion for some of those lower pressure cartridges, but only for comparative purposes. I really can't tell what the absolute pressure is from the ring diameters, and can only make a rough comparison to another load that I have confidence in.

Clark and Unclenick both seem to have moved-on to using strain gauges mounted on THEIR guns to evaluate loads for their guns. That seems like a great idea, but is not so convenient for revolvers, lever guns, and some others. Speer made a special cylinder for a revolver that allowed them to do piezoelectric pressure measurements that showed very different pressure traces between revolvers and test barrels. That just means that, even if we used modified Contender barrels with strain gauges to work-up loads for our own revolvers, we would still be getting different pressures in the revolvers. The advantage over the loads in the load manual would be that we could see the effects of OUR primers, cases, crimps, powder lots, etc. IN THE CONTENDER BARREL. But, the down side is that the Contender barrel is not at SAAMI minimum spec. So, we don't really have the history behind it that is behind the test barrels to tell us that something that is OK in the test is OK in our revolver, too.

So, even with a strain gauge, there are some things that are still just relative measurements.

I don't doubt that you can do more with a strain gauge than you can without one. But, I don't agree that you can use a strain gauge on your gun to prove that Speer or any other manual maker is doing poor work. There are just too many variables that aren't being accounted for.

And, I notice that Clark has switched horses a little, too. I thought he was originally basing his assertions about Speer on his QuickLOAD calculations. That is what pulled me into this thread, because I think it is dangerous to advise other forum members to disregard manual data in favor of calculations. And, that is what Clark really seems to be doing, by saying that Speer data doesn't make any sense so he doesn't use it

SL1

[GeauxTide]

The reference materials will carry you to your experience as you experiment. A good chronograph that provides extreme spread and standard deviation validates or invalidates your experiments. Only computer simulations I like are L4D and Call of Duty.

[Unclenick]

Yeah, but think of all the intellectual stimulation you'd have missed out on.

I tend to load strictly to maximize accuracy. If I can't get an accuracy peak with a load that gives me good case life, I eat the case cost. If I can't get maximum velocity or retained energy with a load that is accurate, I give up on the maximum velocity and retained energy before I will let go of accuracy. In my experience, a gun being badly stressed cannot deliver best accuracy, so this is unlikely to cause a conflict with case or gun life. On the other hand, there are some good accuracy loads in some chamberings that still wear a barrel out pretty fast. You have to choose what matters to you most? I suppose I am old fashioned in embracing Townsend Whelen's maxim that only accurate rifles are interesting.

[Clark]

I just ran across Kevin Adam who has made a video on how to use Quickload:
http://www.youtube.com/watch?v=a3RkvTxW4lE

He is a guy in Scotland with his own gun forum.
http://www.shootforum.com/forum/
He sounds like the voice from the Enterprise's engine room.

[Ko3ak]

Hi all:

First time long time....

I too, like Clark, started loading about 10 years ago, and am an Electrical Engineer, (some would call me nerdy at times).

Likewise, I did start with the included Speer #12 manual found with the RCBS partner press package.

That was and is my ONLY manual in book form. I have looked through #'s 13 and 14 and found very little additions worth the money to by them. So I didn't.

Overall, and empirically speaking, Speer data has served me well. Sure, you have to keep in mind the variations in barrel length, tolerances, case dimensions, powder lots, bullet types, shapes, sizes and all that ad infinitum...

I too am capable of over-engineering, over-anal-izing(yes, I meant the anal reference lol) and seen more often than not with a micrometer and or a portable Fluke meter in hand. However, with freshly made ammo, gun(s) in hand, and the greatest luxury of all - my chronograph, I would strut out to the range and check my work and compare/verify what the book says. In general, more often than not, and with some crude extrapolating my results were just fine. But as always, you start low and then work up.

For me, one dangerous example of bad data in the SPeer #12 and I believe #'s 13 & 14, is the loading for 40 S&W 180 gr GD using Unique. For me, empirically, the STARTING load gave me veocities that were very close to their MAX loads. You know, Glock smilies and stuff.

On-line data from Hodgdon, Alliant, Accurate, and whoever else has served me well as well. So, in concluding my mini rant, I think all of us can, and do get by without spending tons of money on pretty hard-bound loading manuals that look nice on our shelves. The most important things we can do is to always start loading on the low side, and get that all-important negative-feedback loop working for us (I know Clark will appreciate this!). Or, more so in Clark's case that soon out-of-control positive feedback loop!

Oh, and one last thing... and this goes out to Clark: Dude, I've read your posts and perhaps replied to them over the years and found you to be hilarious, well informed - sometimes not, silly, daring, bold, and someone who I could relate to. I even lived not too far away from you over in Renton. I'd peer out to the NW and see how the richees lived.

[Clark]

Nerd to nerd:
When I was 5 years old I could not figure out why inner tubes floated when the air did not touch the water. How did the water know there was air in that tube?
Also when I was 5, I would go to Pacific Car and Foundry in Renton on Saturday with my father to see the guys working overtime on gun designs. I was wearing cap guns in holsters and a cowboy hat. I saw the red hydraulic fluid on the ground and assumed it must be blood from people being shot by those guns.

Like Bertrand Russell injected with adrenaline, feeling fear without object, I feel like a nerdy curiosity for numbers like a real engineer, but lack talent.

If I am on page 278 of Speer 12 and see that 41 gr H4895 max load does 2488 fps and 39 gr IMR4895 max load does 2347 fps, I would infer from that, that H4895 is slower.
Yet on page 288 I see 54.5 gr IMR 4895 max load does 3080 fps and 53 gr H4895 max load does 3076 fps, and I would infer from this that IMR 4895 is slower.
Then someone else pointed out to me that change in velocity/ change in charge was .8 in Speer 12 pistol cartridges, while chronographs make it look more like 1.0.

[SL1]

Clark,

I don't have Speer #12, so, would you please post the cartridges and bullets that gave the apparently "conflicting" relative burning rates in what must be two different cartridges, since they are 10 pages apart?

SL1

[denton]

Those who, for some perverse reason, want to read a bit more of what I have written, can do that here. http://www.snipershide.com/Pressure

Firearms are designed with large safety margins. 99.9% of the time you don't need that margin. When you get a case head separation or some other bad event, you'll be very thankful that it was there. There are shooters that ignore this and use the full safety margin for everyday shooting. While I have no quarrel with people who do that, I do try to avoid shooting next to them at the range.

As a point of interest, I have a beautiful data set from Ken Oehler with four simultaneous measurements on a broad range of pressures, two taken with piezo equipment and two taken with strain gauges. That provided a nice opportunity to test strain vs. piezo accuracy and precision. The brass offset used in piezo measurements is arrived at differently from the brass offset typically used in strain measurements, the piezo method producing a slightly higher estimate of chamber pressure. If you run the piezo data against the strain data, they track nearly perfectly except that the piezo method produces estimates 1,700 PSI above the strain estimate.