Powder charge question

Dragon55 · March 19, 2009, 05:08 PM

I've only loaded about 1000 rounds(so far with no boo boos) using the same basic recipe and have another question. Why when looking at different powders do the charges not change with the same % difference powder to powder?? I have looked at tables from Lee, Alliant, Lyman. The 2 powders I saw a big difference in is Bullseye and Accur#7. From one load to another I see as much as 20% difference. What I mean is Accur#7 only changed 5% and Bullseye changed 21%.(Between 150gr jacketed and 155gr lead)

If the answer is 'These loads have been established through experience, trial and error, or some other subjective testing' then I understand. If it's based on chemistry or physics then I don't understand.

SL1 · March 19, 2009, 05:25 PM

I'm not sure I even understand your question. Are you asking why the %change in MAXIMUM charge weight for two powders when going from bullet weight A to bullet weight B is not the same % value?

If so, the answer has to do with a lot of factors, including the burn rate of the powder, the capacity of the case, the SAAMI pressure limits for the cartridge, and, of course the bullet weights. In some situations, the powder charges don't increase by the same % amount because there just isn't enough room for one of them to have enough powder to get to the pressure limit, but there is for the other. In some cases, the physics/chemistry is more complicated.

SL1

Dragon55 · March 19, 2009, 05:32 PM

For .40 caliber... for example from Lee.....

135gr jacketed bullet Bullseye 7gr charge Accur#7 10.1gr charge

155gr lead bullet Bullseye 4.6gr (that's 66% of 135gr load)
Accur#7 8.7gr (that's 86% of the 135gr load)

I would have expected them to be closer.

SL1 · March 19, 2009, 05:56 PM

Dragon 55,

When you go to the heavier bullet, you are doing TWO things.

One is that you are making the bullet heavier, and that means it moves more slowly as the powder burns. Faster powders get more gas produced while less space is there, so pressure goes up faster than for a slower powder.

Second, the extra bullet weight comes from lead that is INSIDE the case - - the bullet is longer but doesn't stick out any farther because overall cartridge length is limited by gun dimensions. So, that means that there is an INVERSE relationship between bullet weight and powder space.

These two factors, plus the differences in the way the powder burning rate changes with pressure from powder to powder, mean that you should have no reason to expect two powders to have the same % change in maximum charge weight from one bullet weight to another weight.

Assuming that powders work the way you expect can get you into BIG trouble.

SL1

Dragon55 · March 19, 2009, 06:05 PM

I get it.... seems to me to have a lot to do with burn rate differences. I know better than to experiment and wasn't even suggesting that. I was just thinking in a straight line... which I've learned from reading this forum has little to do with reloading. I will probably just stick to what I see on a table from Lee or Lyman in regards to this Bullseye powder I have.

Thanx again... every day I look at this forum and learn something else.

Andrewh · March 19, 2009, 06:45 PM

you also compared two different types of bullets.
A lead round builds up more pressure, so less powder is needed compared to a jacketed round.

But I suspect the proportions will be close as you figured out, the burn rates are different.

tiberius10721 · March 19, 2009, 06:59 PM

why do lead balls build up more pressure?Ive heard of barrel leading using cast lead and i have noticed that powder charges for lead bullets that are the same weight as jacketed bullets are less but i thought it was to prevent leading.Yikes i guess i was wrong.

wncchester · March 19, 2009, 08:10 PM

"If it's based on chemistry or physics then I don't understand."

It is NOT based on any such science. In fact, the changes in burn rate due to varing conditions borders on black magic that can only be casually predicted without experimentaion.

Charges for lead/cast bullets are lower to prevent the softer grip on the lands from stripping out, nothing more.

SL1 · March 19, 2009, 08:23 PM

Actually, pressure with lead bullets is not so simple. For one thing, lead bullets come in a wide variety of hardnesses. Really soft lead (pure) will pretty easily deform. SO, you an shoot it with low pressure loads and it will deform enough AT THE BULLET'S BASE to seal the bore and shoot accurately. But, get the pressure very high and it will expand for the entire length of the bullet and increase pressure more than a bullet that is harder. SO, you are not assured of low pressures with soft bullets if you make the pressure too high. That is especially true with revolvers, where the bullet can sort of "rivet" in the forcing cone and raise pressure as it is swaged back down to bore size.

Harder lead bullets NEED higher pressures to expand properly to seal the bore, and will lead due to gas-cutting at low pressure as the hot gases escape past the bullet. Hard lead bullets (with a good lube) can be driven to very high velocities for a handgun, often faster than jacketed bullets. That is because the lead bullets have lower friction than the copper jackets, and do not deform as much as the soft cores of jacketed bullets at the same pressure.

So, you will see a wide range of charge weights for lead bullets, depending on the lead alloy.

Some jacketed bullets have hard lead cores instead of soft cores because they are designed for really high-pressure cartridges like the 454 Casull.

So, it is really difficult to talk about load comparisons between the lead and jacketed bullets until you take these particulars into account.

SL1

tiberius10721 · March 19, 2009, 09:34 PM

Thanks for the wealth of information about lead bullets.thats why I love these forums

:

James R. Burke · March 22, 2009, 10:43 AM

SL1 has it right and covered pretty good. Seating depth with differnt bullets will no doubt change your % or space in the case doing what SL1 has said.

March 19, 2009, 05:08 PM	#1
Dragon55 Senior Member Join Date: March 15, 2009 Location: East Tennessee Posts: 811	Powder charge question I've only loaded about 1000 rounds(so far with no boo boos) using the same basic recipe and have another question. Why when looking at different powders do the charges not change with the same % difference powder to powder?? I have looked at tables from Lee, Alliant, Lyman. The 2 powders I saw a big difference in is Bullseye and Accur#7. From one load to another I see as much as 20% difference. What I mean is Accur#7 only changed 5% and Bullseye changed 21%.(Between 150gr jacketed and 155gr lead) If the answer is 'These loads have been established through experience, trial and error, or some other subjective testing' then I understand. If it's based on chemistry or physics then I don't understand. __________________ sailing ... A way to spend lots of money and go real S L O W

March 19, 2009, 05:32 PM	#3
Dragon55 Senior Member Join Date: March 15, 2009 Location: East Tennessee Posts: 811	More specific........ For .40 caliber... for example from Lee..... 135gr jacketed bullet Bullseye 7gr charge Accur#7 10.1gr charge 155gr lead bullet Bullseye 4.6gr (that's 66% of 135gr load) Accur#7 8.7gr (that's 86% of the 135gr load) I would have expected them to be closer. __________________ sailing ... A way to spend lots of money and go real S L O W

March 19, 2009, 06:05 PM	#5
Dragon55 Senior Member Join Date: March 15, 2009 Location: East Tennessee Posts: 811	Thanx SL1......... I get it.... seems to me to have a lot to do with burn rate differences. I know better than to experiment and wasn't even suggesting that. I was just thinking in a straight line... which I've learned from reading this forum has little to do with reloading. I will probably just stick to what I see on a table from Lee or Lyman in regards to this Bullseye powder I have. Thanx again... every day I look at this forum and learn something else. __________________ sailing ... A way to spend lots of money and go real S L O W

March 19, 2009, 09:34 PM	#10
tiberius10721 Junior member Join Date: December 22, 2008 Posts: 228	Thanks for the wealth of information about lead bullets.thats why I love these forums:

March 19, 2009, 05:25 PM	#2
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	I'm not sure I even understand your question. Are you asking why the %change in MAXIMUM charge weight for two powders when going from bullet weight A to bullet weight B is not the same % value? If so, the answer has to do with a lot of factors, including the burn rate of the powder, the capacity of the case, the SAAMI pressure limits for the cartridge, and, of course the bullet weights. In some situations, the powder charges don't increase by the same % amount because there just isn't enough room for one of them to have enough powder to get to the pressure limit, but there is for the other. In some cases, the physics/chemistry is more complicated. SL1

March 19, 2009, 05:56 PM	#4
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	Dragon 55, When you go to the heavier bullet, you are doing TWO things. One is that you are making the bullet heavier, and that means it moves more slowly as the powder burns. Faster powders get more gas produced while less space is there, so pressure goes up faster than for a slower powder. Second, the extra bullet weight comes from lead that is INSIDE the case - - the bullet is longer but doesn't stick out any farther because overall cartridge length is limited by gun dimensions. So, that means that there is an INVERSE relationship between bullet weight and powder space. These two factors, plus the differences in the way the powder burning rate changes with pressure from powder to powder, mean that you should have no reason to expect two powders to have the same % change in maximum charge weight from one bullet weight to another weight. Assuming that powders work the way you expect can get you into BIG trouble. SL1

March 19, 2009, 06:45 PM	#6
Andrewh Senior Member Join Date: July 7, 1999 Posts: 966	you also compared two different types of bullets. A lead round builds up more pressure, so less powder is needed compared to a jacketed round. But I suspect the proportions will be close as you figured out, the burn rates are different.

March 19, 2009, 06:59 PM	#7
tiberius10721 Junior member Join Date: December 22, 2008 Posts: 228	why do lead balls build up more pressure?Ive heard of barrel leading using cast lead and i have noticed that powder charges for lead bullets that are the same weight as jacketed bullets are less but i thought it was to prevent leading.Yikes i guess i was wrong.

March 19, 2009, 08:10 PM	#8
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	"If it's based on chemistry or physics then I don't understand." It is NOT based on any such science. In fact, the changes in burn rate due to varing conditions borders on black magic that can only be casually predicted without experimentaion. Charges for lead/cast bullets are lower to prevent the softer grip on the lands from stripping out, nothing more.

March 19, 2009, 08:23 PM	#9
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	Actually, pressure with lead bullets is not so simple. For one thing, lead bullets come in a wide variety of hardnesses. Really soft lead (pure) will pretty easily deform. SO, you an shoot it with low pressure loads and it will deform enough AT THE BULLET'S BASE to seal the bore and shoot accurately. But, get the pressure very high and it will expand for the entire length of the bullet and increase pressure more than a bullet that is harder. SO, you are not assured of low pressures with soft bullets if you make the pressure too high. That is especially true with revolvers, where the bullet can sort of "rivet" in the forcing cone and raise pressure as it is swaged back down to bore size. Harder lead bullets NEED higher pressures to expand properly to seal the bore, and will lead due to gas-cutting at low pressure as the hot gases escape past the bullet. Hard lead bullets (with a good lube) can be driven to very high velocities for a handgun, often faster than jacketed bullets. That is because the lead bullets have lower friction than the copper jackets, and do not deform as much as the soft cores of jacketed bullets at the same pressure. So, you will see a wide range of charge weights for lead bullets, depending on the lead alloy. Some jacketed bullets have hard lead cores instead of soft cores because they are designed for really high-pressure cartridges like the 454 Casull. So, it is really difficult to talk about load comparisons between the lead and jacketed bullets until you take these particulars into account. SL1

March 22, 2009, 10:43 AM	#11
James R. Burke Senior Member Join Date: January 3, 2009 Location: U.P. of Mich/Quinnesec Posts: 1,897	SL1 has it right and covered pretty good. Seating depth with differnt bullets will no doubt change your % or space in the case doing what SL1 has said.