Some data concerns me.
I've just picked up a copy of Lee's Modern Reloading manual second edition of 2003 reprinted 2009. I have been comparing the loads I have been using for many years for my 22-250 and 280 Rem. The manual I have used for many years is the Hodgdon #26 of 1993. Some of Lee's loads have me concerned. For example: I use H380 at 37.0 gr and a 55 gr V-max for groups under a half inch at 100 yds. My Hodgdon manual lists this load as MAX at 54Kcup! The Lee book shows a starting load of 38.0gr and a max of a compressed load of 41.0 gr and 65.1Kpsi. That's a huge difference! Scares me! I tried 38gr in my gun and saw the start of primer flattening and metal flow into the firing pin hole. For the 280 max loads run a little higher too. I load for many calibers and the Lee book is more aggressive throughout. Some loads look risky to me for the inexperienced reloader. I don't believe powders have become milder. And if you're running in the 60k+ neighborhood to get the job done, you're probably using the wrong gun. I'm sticking with my conservative Hodgdon manual!
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For one thing there is quite a bit if difference between CUP and PSI.
Someone will come along and put up the formula for it, maby.
This is what I found[;)] Put thefiringline.com/forums/showthread.php?=207765 in your search.
psi=-17,902+(1.51cup)
cup=(psi+17,902)/1.51
If this helps you.0 -
In truth, there is no reliable conversion formula for CUP to PSI or vice-versa. Compare CUP to CUP and PSI to PSI only.
Second, Lee did not develop or test a single load in their manual. They simply gather, arrange and print data from other sources. Given the possibility of typos both in the originals and then in the reprint, Lee's data should not be overly relied upon.
Hodgdon loads were conservative because of their test methods at the time. They shot a variety of bullets of a given weight and printed the data for the bullet that produced the highest average pressures without exceeding SAAMI maximum. They reasoned that no matter what other bullet the reloader chose to use, he'd be safe. That test method has changed with current Hodgdon manuals, BTW.
Get yourself a current manual for the bullet you choose to shoot. Crosscheck the data therein with the powder maker's data, and then triple-check any discrepancies with the Lyman manual.0 -
quote:I've just picked up a copy of Lee's Modern Reloading manual
That's your first problem
LEE's data is taken from the "public sector" (IE the copyrights have run out) data, than he pee's all over it with his "grain to CC" conversion. NO further testing is done from there.
The best usage for a LEE manual is as "reserve" paper for the outhouse.0 -
quote:Originally posted by Rocky Raab
In truth, there is no reliable conversion formula for CUP to PSI or vice-versa. Compare CUP to CUP and PSI to PSI only.
Second, Lee did not develop or test a single load in their manual. They simply gather, arrange and print data from other sources. Given the possibility of typos both in the originals and then in the reprint, Lee's data should not be overly relied upon.
Hodgdon loads were conservative because of their test methods at the time. They shot a variety of bullets of a given weight and printed the data for the bullet that produced the highest average pressures without exceeding SAAMI maximum. They reasoned that no matter what other bullet the reloader chose to use, he'd be safe. That test method has changed with current Hodgdon manuals, BTW.
Get yourself a current manual for the bullet you choose to shoot. Crosscheck the data therein with the powder maker's data, and then triple-check any discrepancies with the Lyman manual.
+!
Only go cup to cup..psi to psi.
That 22/250 is among the highest pressure rounds there is.
http://www.leverguns.com/articles/saami_pressures.htm0 -
As I understand it psi also considers the duration of the peak pressure which is also a major factor and has contributed to what may appear on the surface as unsafe loads but because of the peak presure duration (or lack of) are not.
It is claimed that psi is a much more reliable (and trackable) method of measurement.0 -
You are nearly correct, dakota. The copper crusher system (CUP) measured absolute peak only. It did not and could not show how fast the pressure rose or decayed. It didn't even measure peak pressure very well, because of the inertial lag in the system and the fact that the copper slug could not deform fast enough to "catch" really short pressure pulses.
Transducer (and newer strain gauge) systems can track and display the pressure rise, peak and decay profiles, seeing even the shortest of pulses - and even pulses within pulses. Think of ripples on a surf roller to grasp that.
What actually counts most for velocity isn't the peak pressure but pressure over time. It's calculated as the area under the pressure curve. If you visualize a short, steep peak and a broad rounded hill, you'll grasp that. The broad hill, even though it hits no higher than the sharp peak, has more space under it. That space is gas volume under pressure, and that's what pushes the bullet at high acceleration. A sharp peak hits it once; a broad hill pushes it for a long time.0
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