Powder Burn, Amount of Powder, Barrel Length - How Does it all add up?

Full-choke · January 30, 2008, 11:28 AM

Okay, so I am getting ready to start reloading for 6mm Remington and 45-7 Government. But, here's the one thing I haven't been able to read about or learn so far. Is there a trick or formula in which you can figure out how many grains of a said powder will burn most efficiently in your barrel. This means not too little of a burn, and not spitting unburnt powder out the end of the barrel. So, is there a method to this madness or is it just sort of a guess and check kind of deal based on load books, etc.? I have some Nosler bullets that I'm planning on cranking out some 6mm Rem loads with. The barrel is 26" long, looking at powders off their website I should use IMR 3031 for both the bullets I have.

Any load help would be helpful...

Thanks,
F-C

AlaskaMike · January 30, 2008, 11:54 AM

It's been shown that even in a rifle the vast majority of the powder is burned in just the first few inches of barrel length. I don't load either of those calibers so I can't really comment directly on them, although from what I've read, 3031 is a very good powder for the .45-70.

My only advice would be to cross-check a given load in other manuals, get a chronograph if you don't already have one, and do some testing. Each gun is different and you need to discover what works best in yours.

Mike

freakshow10mm · January 30, 2008, 12:33 PM

I use IMR4198 and Varget in 45/70 but IMR3031 is a great powder for it.

Quickload has a burn efficiency function.

Generally speaking, the longer the barrel the slower the powder, the shorter the barrel the faster the powder. Especially in handgun.

IMR3031 doesn't have a reputation for not burning completely. Get a 1# sampler and try it out.

brickeyee · January 30, 2008, 12:51 PM

After a few inches of travel the bullet is being accelerated bythe high pressure gas behind it only.
The powder has been completely consumed.

Some fast powders before the heel of the bullet clears the case, but rifle powders normally within a few inches of bullet travel.

The bullet will continue to accelerate as long as the pressure is above the friction of bullet to barrel until it either exits or exceeds the speed of sound in the driving gas.
No object can be driven faster than the speed of sound in the driving gas.

Most rifle calibers can gain additional velocity with a longer barrel (.22 RF being a common exception),

Full-choke · January 30, 2008, 01:28 PM

Okay, so if I'm kind of getting this...too much powder creates too much pressure from the gas and blasts the bullet out the end wildly. Too little powder will create drag from friction, slows the bullet down and doesn't get enough pressure to correctly drive the bullet. The in between, where we like to be, will be the most accurate and has the proper amount of powder to burn and the proper amount of gases to get it out of the barrel?

I think I just talked in a gigantic circle, but I think I'm understanding things...

F-C

Dave P · January 30, 2008, 02:48 PM

"No object can be driven faster than the speed of sound in the driving gas."

Say what??? So how do my bullets approach 2700 fps - do they accelerate after leaving the barrel -- Like magic?

I select a powder that will burn (mostly) completely in the barrel being used. For example, 42 gr of 4064 needs about 24" to burn completely - not just a few inches.

zxcvbob · January 30, 2008, 04:03 PM

Quote:

"No object can be driven faster than the speed of sound in the driving gas."

Say what??? So how do my bullets approach 2700 fps - do they accelerate after leaving the barrel -- Like magic?

I'm not sure, but I think that is a true statement. What is the speed of sound in a gas compressed to, say, 100 atmospheres of pressure? I'll bet it's a lot faster than 1100 fps.

brickeyee · January 30, 2008, 05:29 PM

""No object can be driven faster than the speed of sound in the driving gas."

Say what??? So how do my bullets approach 2700 fps - do they accelerate after leaving the barrel -- Like magic?

I select a powder that will burn (mostly) completely in the barrel being used. For example, 42 gr of 4064 needs about 24" to burn completely - not just a few inches."

If the bullet approached the speed of sound in the driving gases it would set up a mach wave and no more force could be exerted on the bullet.
Do you even know what the speed of sound is in a gas at 50,000+ PSI?

You are confusing powder gases at high pressure that can still accelerate the bullet with burning.
The decompostion (not burning in the common sense) has all occured within a few inches.
After that the hot high pressure gas is just expanding and accelerating the bullet.

saands · January 30, 2008, 06:36 PM

Quote:

You are confusing powder gases at high pressure that can still accelerate the bullet with burning.
The decompostion (not burning in the common sense) has all occured within a few inches.
After that the hot high pressure gas is just expanding and accelerating the bullet.

I tend to agree with the first part, but not the rest ...

Now, I've never gotten inside a chamber and watched, but according to my version of Quickload (which I tend to believe simply because it does a darned good job of predicting reality) a load of 50 gr of 3031 behind a 350gr bullet will only burn 85% of the powder in an 18" guide gun ... and 12% remains unburnt even in a 24" bbl. It IS true that MOST of the powder (most = more than half) is consumed in the first 4.5" ... but even the fastest loads I've run don't burn before the bullet leaves the case.

I have used QL to design/make VERY quiet loads ... I have a 45acp Mauser rifle that I can load with RedDot and get a barely subsonic 300 grain bullet to leave the muzzle with only a few hundred PSI of residual pressure ... THIS load DOES burn completely in the first 1.2 inches ... the rest of the barrel is for acceleration and gas pressure reduction ... Sounds like a loud air rifle but hits with authority.

saands

Ozzieman · January 30, 2008, 08:42 PM

...too much powder creates too much pressure from the gas and blasts the bullet out the end wildly. Too little powder will create drag from friction, slows the bullet down and doesn't get enough pressure to correctly drive the bullet. The in between, where we like to be

Ok first off never load any ammo out side the min/max shown in any good reloading manual.
Personally your description above needs a little work
Too much and the bolt might enter your brain and too little can also do bad things.
The people that write the manuals have much better tools and ways of checking chamber pressures that we cannot afford in many cases can’t get and all of there loads stay inside the max pressures that are listed in the cases that you’re reloading.
I reload both 45/70 and 6 MM rem. If you have not been reloading then start with something easy and use 4895 for the 6mm and take some of the suggestions for the 45/70.
I load black powder in my 45/70s and have never loaded smokeless.
The 6mm I would stay with the lighter bullets (70 GR) and stay at least within the middle load weights of what the manuals suggest as a starting point and don’t worry about where and when the powder is burnt. If in ether case you have a lot of powder burning out side the barrel of the gun,,, then you have a BOMB in your hands.

brickeyee · January 30, 2008, 08:56 PM

If you have quickload you can see the decline in pressure that almost perfectly follows Boyle's law.
Double the volume, halve the pressure.
this means that the production of new gas has ceased.
The remaining gas is simply expanding and driving the bullet.

Residual pressure does not indicate unburned powder, just that the gas still has pressure that can do work.

January 30, 2008, 11:28 AM	#1
Full-choke Senior Member Join Date: May 10, 2007 Location: Ohio Posts: 617	Powder Burn, Amount of Powder, Barrel Length - How Does it all add up? Okay, so I am getting ready to start reloading for 6mm Remington and 45-7 Government. But, here's the one thing I haven't been able to read about or learn so far. Is there a trick or formula in which you can figure out how many grains of a said powder will burn most efficiently in your barrel. This means not too little of a burn, and not spitting unburnt powder out the end of the barrel. So, is there a method to this madness or is it just sort of a guess and check kind of deal based on load books, etc.? I have some Nosler bullets that I'm planning on cranking out some 6mm Rem loads with. The barrel is 26" long, looking at powders off their website I should use IMR 3031 for both the bullets I have. Any load help would be helpful... Thanks, F-C

January 30, 2008, 11:54 AM	#2
AlaskaMike Senior Member Join Date: September 26, 2005 Posts: 947	It's been shown that even in a rifle the vast majority of the powder is burned in just the first few inches of barrel length. I don't load either of those calibers so I can't really comment directly on them, although from what I've read, 3031 is a very good powder for the .45-70. My only advice would be to cross-check a given load in other manuals, get a chronograph if you don't already have one, and do some testing. Each gun is different and you need to discover what works best in yours. Mike

January 30, 2008, 12:33 PM	#3
freakshow10mm Junior member Join Date: January 23, 2008 Location: MI Posts: 1,398	I use IMR4198 and Varget in 45/70 but IMR3031 is a great powder for it. Quickload has a burn efficiency function. Generally speaking, the longer the barrel the slower the powder, the shorter the barrel the faster the powder. Especially in handgun. IMR3031 doesn't have a reputation for not burning completely. Get a 1# sampler and try it out.

January 30, 2008, 12:51 PM	#4
brickeyee Senior Member Join Date: December 29, 2004 Posts: 3,351	After a few inches of travel the bullet is being accelerated bythe high pressure gas behind it only. The powder has been completely consumed. Some fast powders before the heel of the bullet clears the case, but rifle powders normally within a few inches of bullet travel. The bullet will continue to accelerate as long as the pressure is above the friction of bullet to barrel until it either exits or exceeds the speed of sound in the driving gas. No object can be driven faster than the speed of sound in the driving gas. Most rifle calibers can gain additional velocity with a longer barrel (.22 RF being a common exception),

January 30, 2008, 01:28 PM	#5
Full-choke Senior Member Join Date: May 10, 2007 Location: Ohio Posts: 617	Okay, so if I'm kind of getting this...too much powder creates too much pressure from the gas and blasts the bullet out the end wildly. Too little powder will create drag from friction, slows the bullet down and doesn't get enough pressure to correctly drive the bullet. The in between, where we like to be, will be the most accurate and has the proper amount of powder to burn and the proper amount of gases to get it out of the barrel? I think I just talked in a gigantic circle, but I think I'm understanding things... F-C

January 30, 2008, 02:48 PM	#6
Dave P Senior Member Join Date: August 17, 1999 Location: North Florida Posts: 1,351	"No object can be driven faster than the speed of sound in the driving gas." Say what??? So how do my bullets approach 2700 fps - do they accelerate after leaving the barrel -- Like magic? I select a powder that will burn (mostly) completely in the barrel being used. For example, 42 gr of 4064 needs about 24" to burn completely - not just a few inches.

January 30, 2008, 05:29 PM	#8
brickeyee Senior Member Join Date: December 29, 2004 Posts: 3,351	""No object can be driven faster than the speed of sound in the driving gas." Say what??? So how do my bullets approach 2700 fps - do they accelerate after leaving the barrel -- Like magic? I select a powder that will burn (mostly) completely in the barrel being used. For example, 42 gr of 4064 needs about 24" to burn completely - not just a few inches." If the bullet approached the speed of sound in the driving gases it would set up a mach wave and no more force could be exerted on the bullet. Do you even know what the speed of sound is in a gas at 50,000+ PSI? You are confusing powder gases at high pressure that can still accelerate the bullet with burning. The decompostion (not burning in the common sense) has all occured within a few inches. After that the hot high pressure gas is just expanding and accelerating the bullet.

January 30, 2008, 08:42 PM	#10
Ozzieman Senior Member Join Date: December 14, 2004 Location: Northern Indiana Posts: 6,117	...too much powder creates too much pressure from the gas and blasts the bullet out the end wildly. Too little powder will create drag from friction, slows the bullet down and doesn't get enough pressure to correctly drive the bullet. The in between, where we like to be Ok first off never load any ammo out side the min/max shown in any good reloading manual. Personally your description above needs a little work Too much and the bolt might enter your brain and too little can also do bad things. The people that write the manuals have much better tools and ways of checking chamber pressures that we cannot afford in many cases can’t get and all of there loads stay inside the max pressures that are listed in the cases that you’re reloading. I reload both 45/70 and 6 MM rem. If you have not been reloading then start with something easy and use 4895 for the 6mm and take some of the suggestions for the 45/70. I load black powder in my 45/70s and have never loaded smokeless. The 6mm I would stay with the lighter bullets (70 GR) and stay at least within the middle load weights of what the manuals suggest as a starting point and don’t worry about where and when the powder is burnt. If in ether case you have a lot of powder burning out side the barrel of the gun,,, then you have a BOMB in your hands.

January 30, 2008, 08:56 PM	#11
brickeyee Senior Member Join Date: December 29, 2004 Posts: 3,351	If you have quickload you can see the decline in pressure that almost perfectly follows Boyle's law. Double the volume, halve the pressure. this means that the production of new gas has ceased. The remaining gas is simply expanding and driving the bullet. Residual pressure does not indicate unburned powder, just that the gas still has pressure that can do work.