lynn said:
Catshooter
I have never seen that either.
Usually when I am near over pressure my shots climb extremely fast as does my velocity.
What is being described as seeing pressure is usually how I find my best load.
It might be case specific?
Lynn
Lynn...
Actually, I "have" seen the effect, but it is a statistical anomaly. If you repeat the string, it is gone. It comes from the variances in sampling 5 shot groups.
Here's the problem with that "wives tale".
When you add more powder, you:
1 - Reduce the air space in the case.
2 - Increase the surface area of the burning stuff.
1 + 2 = you generate more gas that goes into less space, and since the "Stuff" is progressive burning, it raises pressure faster.
More pressure pushes harder on the bullet thing - so like all inert masses, the more pressure on it, the more faster it goes - there are NO exception to these basic rules of guns.
If you have a ES of 30, then, on average, you will have a velocity distribution all through the 30fps range, like 3000, 3010, 3015, 3020, 3030. For a mean of 3015.
Then we add .5 grains of powder, and we "should" get a distribution statistics of five rounds to be,maybe) 3030, 3040, 3045, 3050, 3060, for a mean average of 3045, or 30~ish fps faster.
But, statistics also allow a distribution statistics of five rounds to be 3030, 3032, 3031, 3034, 3032, and the mean of these is 3031.8... so we say, "Like WOW man, I only got 16.8 fps change, so therefore... bla bla bla..."
But if you run the same string over again, you will never get the same figures.
I have run strings and come up with five velocities that were all the same, i.e., 3407, 3407, 3407, 3407, 3407... so a ES of "0", and an SD of "0". Do you think I'm dumb enough to think I have discovered the best load in the world - not this puppy. Run the same loads,weighed) in the same cases, and it will come out with an ES and SD just like the rest of the loads.
It is easy to be seduced by those magical numbers that pop out of the chronographs - I have been shooting over chrono's since the late 50s... I believe about 80% of what they say.
The light changes, and your 3560fps load is now 3482, or 3795... Duh!
I had a long talk with Ken Oehler about 7 years ago about the absolute accuracy of chronos - mostly the state of the industry, not his stuff.
It was an interesting conversation - most people absolutely believe the numbers that come out of a chrono like they were numbers coming from the National Bureau of Standards.
But they are not - there is no reasonable or practical way to calibrate a chrono, and they ALL use the same $4 clock chip that is made in some country that you have to boil the water before you drink it. :,
The velocities on the same loads vary by the lighting, where the bullet flies through the window, and what the angle the bullet makes over the windows... yet, most shooters think that 3204 in the little window means absolutely, positively, irrevocably, 3204.000000000 feet per second.
It does NOT - Such beliefs are sheer fantasy.
If you want accuracy, you must have a reliable light source with a positive ON/OFF window - as the current chronos work, the circuit board "senses" a soft change in the screen current, because the bullet shape is soft, and the light source is broad. There is no instantaneous on/off... so there is no absolute point that the chrono thinks the bullet is there - it's kinda like the chrono starts getting a hint that something is changing, then at some point, says, "Self, I think a bullet is going through the gate, so lets start timing."
In order to be absolute, the light sheet must be thin,on the order of 1-ish millimeter), and the shadow cast must turn off and on completely - that is, from full light to full dark when the point of the bullet enters the sensing zone.
None of this is practical in a small unit that you can set up at the range.
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And I ain't an old fart - I started loading at 11 years old. I'm just medium aged, like fine wine.
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