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Re: cup to PSI

This topic can be found at:
https://forums.accuratereloading.com/eve/forums/a/tpc/f/2511043/m/2341074

02 December 2004, 06:59
Dutch
Re: cup to PSI
Denton, thanks for posting, but I believe you have made an unacceptable assumption in your work. Two, actually.

Specifically, you assume that the variation is linear. I don't think that is correct.

Second, you assume that the discrepancy between crushers and strain gauges is random error. I do not accept that assumption. The two measure two different things. A strain gauge (or piezo, for that matter) is capable to measure peak PSI much closer to it's true value than a crusher. Simply because of the mechanical delays involved in the crusher system.

The two issues are related, of course.

I would suggest to try both running a non-linear regression, and include the bore expansion ratio of each cartridge as a variable. I would expect at least half of the "error" to disappear.

Oh, and try without the 45/70. There's something fishy about that data point. JMO, Dutch.
02 December 2004, 07:41
DigitalDan
Quote:

Given current methods and practices, the people who write the reloading manuals cannot reliably detect the change due to .25 or even .5 grains of powder, in 30-06 size cases.







Interesting point Denton. I'm not expert at internal ballistics by any means but had come to that conclusion myself some years back. Rather than try to categorize different cases into size groups I simply approach it from the perspective that a percent is a percent is a percent. .5 grain will make a difference in small cases like the Hornet of course, but specific percentage points usually are, 1-2% being detectable over a chronograph with any catridge, at least in my experience.
02 December 2004, 08:45
denton
Quote:

Try kernel regression. Gaussian or Epanechnikov kernel.




We're using something more akin to General Linear Model, which is a subset of those.
02 December 2004, 08:18
<9.3x62>
Try kernel regression. Gaussian or Epanechnikov kernel.
02 December 2004, 12:29
denton
Most of my articles are posted at the RSI site,

http://www.shootingsoftware.com/tech.htm

I hope you enjoy them.

Probably my next investigation will be into the effects of magnum primers in 30 cal rifles. Casual investigation hasn't shown any effects at all, but I want to give them a try at really cold temperatures. The manager of Federal Cartridges 22 rimfire operation also says that he doesn't think there are any... but that's why we do the tests.