The science behind powder and accuracy

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BBQJOE

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I've been reloading over a year now, using Unique, 231, and pistol power.
9mm, 38sp, and .44

But here is something I just don't understand.

I know some powders burn a little faster than others. Some are much cleaner than others, and some are lighter or bulkier.
But we're talking about expanding gasses pushing a piece of metal down a tube.

Given the thought with proper adjustment in powders, you could probably obtain the same amount of pressure pushing the bullet through the barrel with almost any powder.

So if powder A at 6gr gives x amount of pressure, and powder b at 5gr gives the same amount of pressure, how can one be any more accurate than the other?

If this has been discussed, I apologize, but I'm very curious as to what's going on here.
 
Wow, there are whole books written on this subject.

OK, burn rate differs, that changes the pressure curve, that changes barrel harmonics, that changes accuracy.

also what happens to the bullet while it is going down the barrel changes.

there is so much other than just pressure that happens and changes how the accuracy is affected.

If you need real particulars, you might try buying some other reloading manuals.

Check out a good bench rest reloading book. It should explain it all in great detail. The benchrest shooter pay very close attention to all the little picky things. That is how they get those little groups.
 
Although it doesn't exactly answer your question succinctly, Hornady's Ballistics Resource on their web site is a good place to learn a lot more about both internal and external ballistics (internal ballistics is the study of the bullet's action inside the gun; external ballistics while the bullet is in flight; terminal ballistics studies the bullet's behavior upon the target). Very informative, and very professionally presented.
 
Some powders burn more uniformly than others at differing pressues. Powder A may give little variance at 42,000psi(it's sweet spot) but then may vary more than powder B does at 45,000psi(that powder's sweet spot).
And that's just mentioning about consistant powder burn rates at varying pressures, which is all effected by particular calibers and even particular rifles, bullet weights, etc.
Making everthing as consistant as possible is just one key element to getting good accuracy.
 
These are all dynamic systems. Each system is a little different than the next. And then you have humans shooting the things, and they are all different.

Powders do not burn in a linear fashion. The powder curve is exponential. Peak pressures occur at different times. This changes the vibrations of the system.

And don't forget bullets, cases, primers, are all different.

When I thinks about it, I wants to fall asleep.........
 
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