Load data from Berger for 6.5G

[grayfox]

Checking the mathematical engines against known pressure test data is one of the first indicators of whether the particular program is kicking out relevant data.

Hodgdon’s publishes their pressures, but rounded to the nearest 100psi.

A fun one to enter into the internal ballistics models is Hodgdon’s published data on the 90gr TNT on top of Benchmark, a compressed load.

2.200” COL
30.5gr compressed load
90gr TNT
47,000psi

It’s one of the lowest published chamber pressures for a max charge in 6.5 Grendel that I’m aware of. They couldn’t get anymore in the case basically even with a compressed load, at the short COL that is driven by such a short bullet.

An even lower one is this:

90gr TNT
8208XBR
31.0gr Compressed
2.220” COL
42,400psi

Enter those in and see what either of the internal engines kicks out for you.

I'm going to do these, simply as a test, to see what comes out of GRT. I don't have QL so won't so that one...
love these little problems...!

[Zeneffect]

Haven't had benchmark to adjust ba, but input I get for xbr is 45829 with adjusted ba for my lot using ql

default ba is showing 51939 for the xbr load and 2920fps (22" barrel)
adjusted ba is showing ~2800fps

[grayfox]

Ok, in Grt, using the stock 6.5 Grendel model and Benchmark/ 8208 Xbr at the stated loads,
I got Benchmark: 56,108 psi and 104.3% case fill.
For Xbr, 52,674 psi and 103.5% case fill.

So stock Grt models are off by 9,000-10,000 psi as to pressure.
Interestingly enough, the Benchmark (which Grt shows as overpressure) is close to Hodgdon's MV at 2875 fps.
Xbr otoh, while over pressure slightly at 52,674 psi, shows 2883 fps, almost 100 fps faster than Hodgdon.

[LRRPF52]

Ok, in Grt, using the stock 6.5 Grendel model and Benchmark/ 8208 Xbr at the stated loads,
I got Benchmark: 56,108 psi and 104.3% case fill.
For Xbr, 52,674 psi and 103.5% case fill.

So stock Grt models are off by 9,000-10,000 psi as to pressure.
Interestingly enough, the Benchmark (which Grt shows as overpressure) is close to Hodgdon's MV at 2875 fps.
Xbr otoh, while over pressure slightly at 52,674 psi, shows 2883 fps, almost 100 fps faster than Hodgdon.

That’s what I’ve been talking about all these years when we say that QL can be way off. Maybe there are powder/bullet combinations that are closer to reality, but why take a chance when you have published data from industry pillars who used calibrated pressure test breeches?

The big ammunition manufacturers also use pressure test breeches because they have to test their ammo to meet SAAMI MAP, MPLM, and MPSM standards for manufacturers.

There are very specific call-outs in SAAMI for:

Maximum Average Pressure
Maximum Probable Lot Mean
Maximum Probable Sample Mean

None of those numbers but MAP is relevant to hand-loaders. The others are lot-based inspection criteria that help ensure that manufacturers aren’t cranking out large numbers of over-pressured loads.

If a theoretical mathematical internal ballistics engine tells you one number that is many thousands of PSI greater pressure than what is seen in pressure test breech, especially when you match all the variables and plug them into the relevant fields, it not only negates the usefulness of that program/software, but can lead to significant safety problems with said software when it is used against the warnings of the developers.

In these 2 cases, it showed 9,108psi higher for Benchmark, and 10,274psi higher for 8208XBR under the 90gr TNT. This would steer the user in the direction of loading much more conservatively, which is better than loading over by the same factors. There were enough combinations that were over or under by 10,000-20,000psi as to make QL more of a developer’s industry professional tool once calibrated with pressure test data, not really useful for the end-user at home trying to figure out loads or adjust seating depth.

This isn’t me trashing QL or any mathematical engine, just calling out what several developers have experienced and measured against test breeches.

We have worked very hard to promote the safe distribution of reloading data for 6.5 Grendel, and thankfully not seen many instances of catastrophic failures.

We wanted to avoid the trend in new cartridge introduction where hand-loaders with no pressure data keep pushing and pushing until they see “pressure signs”, then back off by an arbitrary grain figure and call it good, then complain when they see actual SAAMI data that was developed professionally and carefully. You also want to have a cartridge that generates sufficient velocity to be appealing and actually useful for its intended purposes.

I know Bill was very adamant about that, and did extensive due diligence in that respect with that initial AA load data that was published to support the cartridge once he got brass turned on from Lapua.

[grayfox]

And I agree with what you're saying, but in honesty since I haven't seen or evaluated anyone's QL program and their tweaks (I'm using Grt here), I can't categorically say their implementations are inherently bad or off - (I can say I'm basically skeptical, which is how I treat my grt results). Example, I do believe that Klem has said he uses his after having made several adjustments and views it as an info-only estimate... I don't use any of his data however. But your points here are absolutely well-taken to be sure.

As part of my career I was a senior license instructor/engineer for several full-scale reactor plant real-time operating simulators - ie, real-time complex math-model simulators of particular designs of nuclear reactor plants, the whole she-bang all the way from neutron fissions to putting 1000 MWe "electricity" on to "the grid". (I also have, as part of my career, operated, started-up from subcriticality to full power and shut-down real nuclear reactors literally hundreds of times, so I think I am knowledgeable in this area.) These simulators had a slew of full-time engineers and math-PhD's to evaluate, maintain and tweak/modify and they were very good simulator-models. But in the final analysis they were models only ("nature doesn't always read your script!!"). The real mcCoy's didn't have to act exactly as the models did. And I have 2 very explicit cases where operators followed what the "models" had told them yet missed what the "real" plant was doing... which in the case of large nuclear reactors, can be serious indeed.
So... math models are just that - models.
The real-deal data trumps anything a model might try to tell us.

btw, thanks for all the hard work you and your guys did to bring out the Grendel handbooks - they have been a great source for me, and if some may not appreciate what it took to do that, I just wanted to say that there are many of us that do.

[LRRPF52]

And I agree with what you're saying, but in honesty since I haven't seen or evaluated anyone's QL program and their tweaks (I'm using Grt here), I can't categorically say their implementations are inherently bad or off - (I can say I'm basically skeptical, which is how I treat my grt results). Example, I do believe that Klem has said he uses his after having made several adjustments and views it as an info-only estimate... I don't use any of his data however. But your points here are absolutely well-taken to be sure.

As part of my career I was a senior license instructor/engineer for several full-scale reactor plant real-time operating simulators - ie, real-time complex math-model simulators of particular designs of nuclear reactor plants, the whole she-bang all the way from neutron fissions to putting 1000 MWe "electricity" on to "the grid". (I also have, as part of my career, operated, started-up from subcriticality to full power and shut-down real nuclear reactors literally hundreds of times, so I think I am knowledgeable in this area.) These simulators had a slew of full-time engineers and math-PhD's to evaluate, maintain and tweak/modify and they were very good simulator-models. But in the final analysis they were models only ("nature doesn't always read your script!!"). The real mcCoy's didn't have to act exactly as the models did. And I have 2 very explicit cases where operators followed what the "models" had told them yet missed what the "real" plant was doing... which in the case of large nuclear reactors, can be serious indeed.
So... math models are just that - models.
The real-deal data trumps anything a model might try to tell us.

btw, thanks for all the hard work you and your guys did to bring out the Grendel handbooks - they have been a great source for me, and if some may not appreciate what it took to do that, I just wanted to say that there are many of us that do.

Thank you for your kind words.

My uncle worked at Hanford Site doing that sort of work, while my dad was an aerospace engineer/mathematician/physicist for USAF/DoD. From as early as I could walk, I got a constant education in applied physics and math, in addition to instruction from my Douglas Aerospace machinist grandfather on cartridges, reloading, and firearms. I took it to a pretty extreme level as a kid in my teens with aerospace especially, and could ask and learn from all the professionals in my neighborhood at the time. That included calculating pretty complex equations for aerodynamic and kinetic performance of aircraft, where I was building atmospheric-variable diagrams for aircraft climb rates, instantaneous vs sustained turn rates, combat radii, and things like that.

My dad was able to assist me since he worked on theoretical flight model envelopes with NATO AeroEs when we were in West Germany helping on the EuroFighter program. I’ve always been passionate about developmental and cutting edge technologies primarily related to aerospace. These interests took far greater priority over whatever distractions were assigned to me in classrooms, not that I had any academic problems, but those were meaningless in comparison to my interests. Pilots were the raw performance checkers who could look at the engineers/mathematicians and say, “Yeah, we tried that and it does/doesn’t work.” It was very informative to watch all those types working together on developmental programs and see the nuances between theory and real world. The pilots are the ones with their lives on the line, so they tend to be very blunt, which is a healthy perspective to have. Most of these guys were AeroEs or MEs who went through USAF Test Pilot School as well, so they had endured academic rigor that every one of them describe as next to soul-crushing, interrupted often each day with test flights of dozens of different types of aircraft.

Bill Alexander is a joy to converse with in this regard, because he has extensive training and experience from UK MoD and his own independent efforts in firearms engineering, testing, development, and all the things he encountered over the years “stuffing different cartridges into the AR-15”. There was so much going on with the AR-15 that I was unaware of but thought I knew, that really pops up when you try to chamber it in something different.

One of the authors of the Grendel handbooks (and fellow forum member) did developmental weapons DoD work at Livermore Labs after his USAF pilot experience in SEA, and one of the other authors is a PhD who did the terminal ballistics testing, photography, and charts showing expansion threshold behavior.

So I have a very lifelong appreciation for engineers, academics, and hands-on technicians in the fields of mathematics and physics, especially the ones who are tasked with applying those to solving very consequential real-world problems.

Would love to hear your insight into Chernobyl some time, not to side track.