Load data from Berger for 6.5G

[MikeyMosin]

thanks for the info, Ive been checking on Leverevolution but havent seen it in stock anywhere yet, I hear this is one of the best powders to use with heavier grain projectiles. Im going to grab a few boxes of bullets ranging from 85 to 123 when I see some in stock. I havent shot the rifle yet so I really dont know what its going to like eating. Its an 18" odin works barrel with a matched bolt on an areo upper. I really like the rifle only problem is when i put the optic on it she weighed in at 9.6 pounds

[LRRPF52]

[Kosh65]

[Zeneffect]

The short answer is no. The reasons are due to endless variables and no way to actually control them to make the requisite constants for said formula. In a lab, sure. In the real world, nope, not to the degree of accuracy to "ride the edge" and say for certain you will be at or under max pressure at all times.

To LRRPF52's point, how do you know your chamber pressure to begin with? I'm pretty much guessing at mine while cross referencing data points... it makes me feel good about "not being over pressure" but the reality is, I don't know if the cat in the box is dead or alive and can only make an assumption based on external observations (which pretty much all manifest after you have gone way over 52k)

[grayfox]

In terms of an "accurate" estimate, and since you don't know your actual starting pressure, and it's primarily a theoretical issue anyway... and it will depend upon, among other things, which powder/bullet/case/primer combo you use, what your actual chamber sizing is, which increment of 0.005" you are doing (ie, how close you are to compression), etc etc etc for - idk - maybe 20-30 other parameters... o yeah and how warm your chamber is...

The answer as to a "formula" is either QL or GRT, both of which are mathematical models that depend heavily on all the input parameters (many input parameters) and on how much you trust their results...
One prediction from GRT with a 100 gr nosler BT and xbr that I have modeled... if you were "only" at 99.6% fill the pressure increase is ~200-300 psi. But if you were at 100.6% capacity the pressure goes up 2000 psi.

These are only mathematical estimates and have not been validated in any way by real pressure testing, but there you go. As always, ym WILL v.
Now the question here is, are you at 99.6% full or 100.6% full? That's another factor I don't think we've been able to measure precisely at the bench.
Both of those models, QL and GRT, are relatively complex models.

Most guys use an MV ladder and study the results to see what their loads are doing for them.

[lazyengineer]

Intersting thread, not sure why the resurrection of it.

Regarding Berger - in my own analysis 130 and 140 seem a bit heavy for ideal Grendel ballistics. 140 doesn't look so great at all to me. And Berger is a very premium very expensive, bullet. Why pay premium for a sub-premium sub-optimal load?

As to QL, I've been running Gordon's, and don't really trust its Grendel results very much. It indicates gross overpressure on common loads, and so using it just causes angst in my experience. I think these tools are more curve-fits than their developers care to admit. Extrapolation into cartridges they didn't specifically curve fit can get goofy.

[LRRPF52]

[LRRPF52]

Intersting thread, not sure why the resurrection of it.

Regarding Berger - in my own analysis 130 and 140 seem a bit heavy for ideal Grendel ballistics. 140 doesn't look so great at all to me. And Berger is a very premium very expensive, bullet. Why pay premium for a sub-premium sub-optimal load?

As to QL, I've been running Gordon's, and don't really trust its Grendel results very much. It indicates gross overpressure on common loads, and so using it just causes angst in my experience. I think these tools are more curve-fits than their developers care to admit. Extrapolation into cartridges they didn't specifically curve fit can get goofy.

[LRRPF52]

[Kosh65]

Thanks for the replies. I figured that the variables would most likely be to great.

[grayfox]

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.

[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.