Another "Shelf Life" Post - Page 2

**Unclenick** · January 2, 2023, 06:22 PM

What the powder manufacturers measure as burn rate for blending or for specifying a powder and what you find on relative burn rate charts are two different things. The manufacturers' measure has been done several ways, with closed bombs, Strand burners, deduction of burn rate from vivacity bomb results, or igniting a standard quantity of powder with a standard quantity of PETN over a water pool. The end results in each case is a burn rate in inches or meters per second for a fixed quantity of powder under a fixed set of pressure conditions. You can read about some of these here and some other methods here.

The results of the above testing are not usually published. Part of the reason is it would mislead the handloader to think he had a number for helping determine a powder charge, but he wouldn't. The reason is that powder characteristics other than just the burn rate affect the pressure it produces. These include the total chemical energy content of the powder and the temperature at which it burns, the ratio of specific heat, its relative progressivity, etc.

An attempt to get all those factors collected under one roof is the relative burn rate. This is what you get in a powder chart. It is based on pretending all powder factors except the burn rate are equal between different powders. The way it works is described in the 2013 Norma manual on page 89, where a relative burn rate chart developed by Bofors is provided. They selected a single cartridge and bullet and primer. They pick a charge weight based on a powder they call the reference. They then load the same charge weight for all the powders they will test into that same cartridge under that same bullet, and what they call the relative burn rate is then just the order of the peak pressures produced.

Jim Watson · January 2, 2023, 08:21 PM

Interesting. Fine details are over my head but it looks like those chaps on the Subcontinent described some methods that would be prompt enough to use for grading a mass produced material almost on the fly or certainly soon enough after a production run to be of use.

**44 AMP** · January 4, 2023, 12:03 AM

I spent 15 years being certified in the AMU (Aqueous Make Up) processes used in a spent nuclear fuel reprocessing plant.

Not identical to smokeless powder manufacture (though a few of the same chemicals were used) but it taught me the basics of industrial chemical make up and certain things are generally common to all of them.

One of them we called "butting". Someone else might call it "blending". Basically, you made up the batch, following the instructions x amount of this, y amount of that, xyz amount of something else, etc. THOROUGHLY mixed so you got a representative sample.

Sample analyzed against lab standard specs. IF your batch was out of spec in some way, you calculated the proper amount of which material you needed to add to "butt" the mixture back into spec.

Added the "butt" the resampled. Sometimes you might butt a tank several times, and sometimes you never did get it right and the whole thing became waste. Where I was doing it, we wound up having to waste more due to time pressure, because what we were making up had to be both right, chemically, and on time to feed a continuous process, and sometimes, we had to "sewer it" (special chem sewer) in order to have the time to re do it, and get it right so we didn't have to shut down the entire plant process.

A powder maker generally, isn't under that kind of time pressure, so, if they have the storage space, they can keep an out of spec batch and keep butting it until they do get it in spec.

January 2, 2023, 06:22 PM	#26
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	What the powder manufacturers measure as burn rate for blending or for specifying a powder and what you find on relative burn rate charts are two different things. The manufacturers' measure has been done several ways, with closed bombs, Strand burners, deduction of burn rate from vivacity bomb results, or igniting a standard quantity of powder with a standard quantity of PETN over a water pool. The end results in each case is a burn rate in inches or meters per second for a fixed quantity of powder under a fixed set of pressure conditions. You can read about some of these here and some other methods here. The results of the above testing are not usually published. Part of the reason is it would mislead the handloader to think he had a number for helping determine a powder charge, but he wouldn't. The reason is that powder characteristics other than just the burn rate affect the pressure it produces. These include the total chemical energy content of the powder and the temperature at which it burns, the ratio of specific heat, its relative progressivity, etc. An attempt to get all those factors collected under one roof is the relative burn rate. This is what you get in a powder chart. It is based on pretending all powder factors except the burn rate are equal between different powders. The way it works is described in the 2013 Norma manual on page 89, where a relative burn rate chart developed by Bofors is provided. They selected a single cartridge and bullet and primer. They pick a charge weight based on a powder they call the reference. They then load the same charge weight for all the powders they will test into that same cartridge under that same bullet, and what they call the relative burn rate is then just the order of the peak pressures produced. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

January 4, 2023, 12:03 AM	#28
44 AMP Staff Join Date: March 11, 2006 Location: Upper US Posts: 28,860	I spent 15 years being certified in the AMU (Aqueous Make Up) processes used in a spent nuclear fuel reprocessing plant. Not identical to smokeless powder manufacture (though a few of the same chemicals were used) but it taught me the basics of industrial chemical make up and certain things are generally common to all of them. One of them we called "butting". Someone else might call it "blending". Basically, you made up the batch, following the instructions x amount of this, y amount of that, xyz amount of something else, etc. THOROUGHLY mixed so you got a representative sample. Sample analyzed against lab standard specs. IF your batch was out of spec in some way, you calculated the proper amount of which material you needed to add to "butt" the mixture back into spec. Added the "butt" the resampled. Sometimes you might butt a tank several times, and sometimes you never did get it right and the whole thing became waste. Where I was doing it, we wound up having to waste more due to time pressure, because what we were making up had to be both right, chemically, and on time to feed a continuous process, and sometimes, we had to "sewer it" (special chem sewer) in order to have the time to re do it, and get it right so we didn't have to shut down the entire plant process. A powder maker generally, isn't under that kind of time pressure, so, if they have the storage space, they can keep an out of spec batch and keep butting it until they do get it in spec. __________________ All else being equal (and it almost never is) bigger bullets tend to work better.

January 2, 2023, 08:21 PM	#27
Jim Watson Senior Member Join Date: October 25, 2001 Location: Alabama Posts: 18,545	Interesting. Fine details are over my head but it looks like those chaps on the Subcontinent described some methods that would be prompt enough to use for grading a mass produced material almost on the fly or certainly soon enough after a production run to be of use.