Extrapolating Charge Weight

[forty_caliber]

Back from the range. Here are the raw results from the LabRadar.

There were no pressure signs that I could detect after firing other than the brass in the 37gr load was very slightly more difficult to eject. The 37gr load was more accurate than any of the others.



I'd appreciate any feedback that you may have on the data.

.40

 

[BC17A]

37 looks great and likely very close to a best performing load. If you are looking to dial it in from there, I'd load some at 36.8, 37.2, 37.4 and maybe 37.6 to see if it'll get even better.

 

[rfwobbly]

Pressure versus OAL, and pressure versus load for (some) handgun powders, in the link below are distinctly linear. See page 3 for charts.

http://www.castpics.net/LoadData/Freebies/RM/Ramshot/Ramshot_3.pdf

Once again some forum experts' claims appear to be disproven by facts.

I don't believe this is what I've said or intended. The Ramshot plots referenced above all fall within the "safe loading zone" for standard chamber pressures. Within those safe loading zones the plot may well be straight, and I certainly trust Ramsot's data.

• My contention is that when you go higher than normal chamber pressures the plot may well bend upward to a more vertical position. This is the "curve" I'm talking about. Let's see the Ramshot plots extended to 70,000 psi and I think the plots will be anything but straight. I have no data in this area myself, but I suspect this is why 0.1gr more powder can turn an uncomfortable Max Load into a catastrophic "kaboom".

• Secondly, Ramshot has plotted 3 powders. That is "proof" of 3 powders, but certainly not proof of ALL powders. In your rush to condemn you may have overlooked this fact.

All the best.

 

[lordpaxman]

I'd appreciate any feedback that you may have on the data.

I often review my chrono data but rely on the grouping to establish the best load. In this case you said the most accurate was the one with the lower ES. That doesn’t often happen with my load development for pistol calibers.
You didn’t say what the sample size was, so there may be a confidence question with the stats, but here’s what I would observe.
There was a trend of lower ES as the charge increased, best guess is a more efficient burn.
There was also a delta of average FPS that was 34, 30 and 38. IMO, the extra grain of powder was producing a higher velocity for each increase. If the last delta was something like 2, I’d be worried that the extra grain of powder only increased the average by such a small amount compared to the others, and would stop there. You’re also knocking on the door of the 440 gr velocity. If it were me, I’d wouldn’t go fishing and call the 37gr good. Good luck!