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Ammo and Reloading Factory Ammunition, Reloading, Components, Load Data and more. |
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#1
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Bullet weights and amount of powder.
I have been loading for a year or so ,using data by the book.
What I want to understand is the pressure and physics of bullet weight requiring a specific powder grain charge. Seems the lighter the bullet the more grains of powder(same brand same type) is required. Conversly the heavier bullet requires less powder. Reading online comments , some relate to larger size bullets as compaired to smaller. Example 9mm virsus 45 acp. What data shows is the "less and more" requirment applies to the same caliber.So a 9mm bullet of 115gr will need more powder than a 147gr bullet. I'm thinking it itakes more pessure to push a lighter bullet than one that is heavier . I'm sure there are other things involved. Anyone got info to enlighten me . |
#2
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The lighter projectile has a great get-up and go factor (Horsepower) and the pressure has to chase it out of the barrel. Whereas the heavier projectile is a bit harder to get going (Torque) and the pressure is slow and steady all the way out.
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#3
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My feed back is a generalization for communication purposes only.
It's not so much 'required' as 'safely capable of'. You're also completely ignoring the velocity aspect of 9x19 vs 45ACP. Logic and physics would dictate that more powder would be needed to push a heavier bullet to the same velocity a lighter bullet and lesser powder would achieve. Lighter bullet allows for higher charge and yet remains in the safe pressure zone. Heavier bullets have more bearing surface and harder to push thru the bore so less powder would keep it in safe pressure zone but velocity suffers. My 115gr JHP 9x19 load runs at around 1150fps with 4.8grs of HP38. My 230gr FMJ 45ACP load runs at around 820fps with the same 4.8gr of HP38. Now factor in burn rate. Slower burning powder takes longer to achieve peak pressure so it's safer to use a little more of it. Fast burning powder achieves peak pressure sooner so less is safer.
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GCC NRA Certified Pistol Instructor Don't count your hits and congratulate yourself, count your misses and know why. |
#4
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Pressure is not what propels the bullet. Rather, it is the energy of the combustion of powder. Pressure is a byproduct of the combustion. Unfortunately, there is only so much powder you can put behind a heavy bullet before the pressure gets too high. Within that pressure limit, you can only generate so much energy to get 1000 FPS out of a 147gr bullet in a 9mm pistol. With a lighter bullet you can stuff more powder behind it to get a higher velocity before the pressure gets too high.
If pressure was what propelled the bullet, then all bullet weights would reach the same velocity at 35,000 PSI. But they don't. |
#5
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All of the above is why we have the "powder trinity." Fast, medium & slow. The classic is Bullseye, Unique and 2400/H110/W296.
I kind of every time the "best powder for calibers A,B,C,D,X,Y & Z" thread rears it's head. Some powders are pretty versatile but you're probably not going to get your best performance in, say, 9mm and .357 Magnum out of the same powder, or even the same caliber with light & heavy bullets.
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