Load data from Berger for 6.5G

[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.