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October 3rd, 2025
SUMMARY: Powder can have a very long shelf life. You need to watch for changes in smell and color. A reddish tinge, almost like rust on the powder, is a bad sign, as is a foul odor, not to be confused with a normal chemical smell. Either of these signs indicate it is time to dispose of your powder by means other than shooting.
Ever wondered about the stability of the propellants in your reloading room? There are some important things you should know about powder storage, to ensure consistent powder performance and safety. Western Powders (which has been acquired by Hodgdon) published an informative Q & A series entitled Dear Labby: Questions for our Ballistics Lab . Here are some excerpts that pertain to powder storage and shelf life. Worried that your powder may be too old? Western’s experts explain how to check your propellants for warning signs.
Proper Powder Storage
Q: I live in southern Arizona where it is very hot. I am told powders will become unstable if stored in an area not air-conditioned. My wife says no powder or primers in the house. Can powder be stored in a refrigerator? What about using a fireproof safe? I would appreciate your ideas. — M.C.
Lab Answer: SAAMI guidelines are pretty clear on issues of storage. They recommend storing smokeless powder in containers that will not allow pressure to build if the powder is ignited — ruling out gun safes and refrigerators.
CLICK HERE to Read SAAMI Guidelines for Powder Storage (PDF)
In their original containers, the lifespan of smokeless powders is quite long, even in hot, arid climates. In fact the lifespan is typically longer than the average handloader would need to store them. Stored safely in a garage or outbuilding, your powder should last years. If you see the powder developing a reddish tint, or giving off a foul odor, it is time to discard it.
Clumps in Powder Container
Q: I ordered some of your Accurate 1680 powder back about in December. I just now opened it … and it is full of clumps. My knowledge tells me that means moisture. Am I wrong? I just now broke the seal and it has been stored in a ammo can with desiccant packs around it and a dehumidifier running 14-16 hours a day. I can’t imagine this being my fault, if this does indicate moisture. I don’t know if the pink part on the label is suppose to be red or not, but it is definitely pink, so if it was red I am wondering if I was shipped an old container? I hope that this isn’t bad and I am stuck with it…
Lab Answer: All powder contains a certain amount of moisture. When the powder is stored or during shipping, it can go through temperature cycles. During the cycling, the moisture can be pulled to the surface and cause clumping. Clumping can also be caused by static electricity if too dry or the powder has limited graphite content. You can break up the clumps before metering and they shouldn’t be a problem. This will not affect the powder performance, so your product is fine. Accurate 1680 labels are designed in Pink. As a side note, specification for testing powder is at 70° F and 60% humidity.
Shelf Life and Packaging Dates
Q: Does powder ever get to old to use and what identifying marks does your company put on the canister for when it is made, You have helped me out a while ago when I asked about keeping my cowboy shooting under 950 fps and it works great less stress on the hand and the recoil is very minimum. — R.B.
Lab Answer: On one pound bottles, the number is on the corner in a silver box. If the powder was poured today, it would read 012815 followed by a lot number. The whole number would look something like 012815749. Eight pound bottles have a sticker on the bottom with an obvious date code. The lot number appears above the date.
August 16th, 2025
POWDER GRAIN SHAPES — What You Need to Know
The shape of powder grains has a profound effect on the performance of the powder charge, as it concerns both pressure and velocity. There are multiple powder shapes including flake, ball, and extruded or “stick” (both solid and perforated).
So how does powder grain shape affect pressure and muzzle velocity?
In general, it can be said that powder that burns progressively achieves a desired muzzle velocity at lower maximum pressure than a powder that burns neutrally, not to mention a degressive powder. As grain size increases, the maximum pressure moves towards the muzzle, also increasing muzzle blast. Muzzle velocity and pressure can be adjusted by means of the amount of powder or loading density, i.e. the relationship between the powder mass and the volume available to it. As the loading density increases, maximum pressure grows.
All Vihtavuori reloading powders are of the cylindrical, single-perforated extruded stick type. The differences in burning rate between the powders depend on the size of the grain, the wall thickness of the cylinder, the surface coating and the composition. Cylindrical extruded powders can also have multi-perforated grains. The most common types are the 7- and 19-perforated varieties. A multi-perforated powder grain is naturally of a much larger size than one with a single perforation, and is typically used for large caliber ammunition.
Other types of powder grain shapes include sphere or ball, and flake. The ball grains are typically used in automatic firearms but also in rifles and handguns. The ball grain is less costly to produce, as it is not pressed into shape like cylindrical grains. Flake shaped grains are typically used in shotgun loadings.
Web thickness in gunpowder terminology means the minimum distance that the combustion zones can travel within the powder grain without encountering each other. In spherical powders, this distance is the diameter of the “ball”; in flake powder it is the thickness of the flake; and in multi-perforated extruded powders it is the minimum distance (i.e. wall thickness) between the perforations.
The burning rate of powder composed of grains without any perforations or surface treatment is related to the surface area of the grain available for burning at any given pressure level. The change in the surface area that is burning during combustion is described by a so-called form function. If the surface area increases, the form function does likewise and its behavior is termed progressive. If the form function decreases, its behavior is said to be degressive. If the flame area remains constant throughout the combustion process, we describe it as “neutral” behavior.
The cylindrical, perforated powders are progressive; the burning rate increases as the surface area increases, and the pressure builds up slower, increasing until it reaches its peak and then collapses. Flake and ball grains are degressive; the total powder surface area and pressure are at their peak at ignition, decreasing as the combustion progresses.
This article originally appeared on the Vihtavuori Website.
March 2nd, 2025
Story by Boyd Allen
While many top competitive shooters trickle their stick powder charges to a kernel or two, that would be impractical when loading charges for giant naval guns. You may be surprised, but the shells fired by the U.S. Navy’s massive 14″ and 16″ naval guns were also propelled by stick-type extruded powders. You couldn’t trickle these ‘kernels’ though — a single stick or ‘grain’ can be over 2″ long.
The U.S.S. Iowa fires her massive 16″ main battery. The U.S. Navy’s Iowa-class battleships carried nine huge 16-inch Mark 7 cannons in three turrets. The big naval guns were 50 calibers long, i.e. 50 times bore diameter, making the barrels 66.7 feet long from chamber to muzzle. |
In connection with a Benchrest Central discussion that drifted to the subject of powders used in large naval guns, I heard from Joe McNeil, whose father was involved in manufacturing those very propellants as a DuPont employee. Joe writes:
“My Dad worked for the DuPont company for over 40 years. Every time the nation went to war he was assigned to the gun powder plants which DuPont ran for the government for $1.00 per year! His last assignment was at the Indiana Ordnance Plant in Jefferson, Indiana from 1952 through 1958. He had a display case made of all of the different powders made at the plant and left it to me. That’s why I have a grain of 16″ gun powder. He took me out to the Jefferson proving grounds once when they tested the powder in a 16″ gun. We watched from a half-mile away but it left a lasting impression when they fired that gun. They actually had a set of rings they fired through to test the performance of the powder and shell. This was a truly fond memory of my Dad and his work.”
Here are some pictures of the gun powder “grains” made during the Korean War at the Indiana Ordnance Works where Joe McNeil’s father worked.
Above is the display case with the different powders manufactured at the DuPont plant. They include: 37 MM/AA, 75MM Pack Howitzer, 50 Cal. 5010, 20 MM 4831, 30 Cal. 4895, 76 MM, 3″, 5″, 90 MM, 4.7″, 240MM, 8″, 280 MM, 175 MM, 155 MM Howitzer, 155 MM Gun M.P., 8″ Gun M.P., 12″, 14, 16″. There are different-sized ‘grains’ for specific rounds.
16-inch/50-caliber gun projectile plus six propellant bags. Display mockup aboard U.S.S. Iowa (BB-61) in San Pedro, CA. Photo by James Madison per Creative Commons CC-BY-SA-4.0 license.
February 19th, 2025
POWDER GRAIN SHAPES — What You Need to Know
The shape of powder grains has a profound effect on the performance of the powder charge, as it concerns both pressure and velocity. There are multiple powder shapes including flake, ball, and extruded or “stick” (both solid and perforated).
So how does powder grain shape affect pressure and muzzle velocity?
In general, it can be said that powder that burns progressively achieves a desired muzzle velocity at lower maximum pressure than a powder that burns neutrally, not to mention a degressive powder. As grain size increases, the maximum pressure moves towards the muzzle, also increasing muzzle blast. Muzzle velocity and pressure can be adjusted by means of the amount of powder or loading density, i.e. the relationship between the powder mass and the volume available to it. As the loading density increases, maximum pressure grows.
All Vihtavuori reloading powders are of the cylindrical, single-perforated extruded stick type. The differences in burning rate between the powders depend on the size of the grain, the wall thickness of the cylinder, the surface coating and the composition. Cylindrical extruded powders can also have multi-perforated grains. The most common types are the 7- and 19-perforated varieties. A multi-perforated powder grain is naturally of a much larger size than one with a single perforation, and is typically used for large caliber ammunition.
Other types of powder grain shapes include sphere or ball, and flake. The ball grains are typically used in automatic firearms but also in rifles and handguns. The ball grain is less costly to produce, as it is not pressed into shape like cylindrical grains. Flake shaped grains are typically used in shotgun loadings.
Web thickness in gunpowder terminology means the minimum distance that the combustion zones can travel within the powder grain without encountering each other. In spherical powders, this distance is the diameter of the “ball”; in flake powder it is the thickness of the flake; and in multi-perforated extruded powders it is the minimum distance (i.e. wall thickness) between the perforations.
The burning rate of powder composed of grains without any perforations or surface treatment is related to the surface area of the grain available for burning at any given pressure level. The change in the surface area that is burning during combustion is described by a so-called form function. If the surface area increases, the form function does likewise and its behavior is termed progressive. If the form function decreases, its behavior is said to be degressive. If the flame area remains constant throughout the combustion process, we describe it as “neutral” behavior.
The cylindrical, perforated powders are progressive; the burning rate increases as the surface area increases, and the pressure builds up slower, increasing until it reaches its peak and then collapses. Flake and ball grains are degressive; the total powder surface area and pressure are at their peak at ignition, decreasing as the combustion progresses.
This article originally appeared on the Vihtavuori Website.
March 7th, 2024
POWDER GRAIN SHAPES — What You Need to Know
The shape of powder grains has a profound effect on the performance of the powder charge, as it concerns both pressure and velocity. There are multiple powder shapes including flake, ball, and extruded or “stick” (both solid and perforated).
So how does powder grain shape affect pressure and muzzle velocity?
In general, it can be said that powder that burns progressively achieves a desired muzzle velocity at lower maximum pressure than a powder that burns neutrally, not to mention a degressive powder. As grain size increases, the maximum pressure moves towards the muzzle, also increasing muzzle blast. Muzzle velocity and pressure can be adjusted by means of the amount of powder or loading density, i.e. the relationship between the powder mass and the volume available to it. As the loading density increases, maximum pressure grows.
All Vihtavuori reloading powders are of the cylindrical, single-perforated extruded stick type. The differences in burning rate between the powders depend on the size of the grain, the wall thickness of the cylinder, the surface coating and the composition. Cylindrical extruded powders can also have multi-perforated grains. The most common types are the 7- and 19-perforated varieties. A multi-perforated powder grain is naturally of a much larger size than one with a single perforation, and is typically used for large caliber ammunition.
Other types of powder grain shapes include sphere or ball, and flake. The ball grains are typically used in automatic firearms but also in rifles and handguns. The ball grain is less costly to produce, as it is not pressed into shape like cylindrical grains. Flake shaped grains are typically used in shotgun loadings.
Web thickness in gunpowder terminology means the minimum distance that the combustion zones can travel within the powder grain without encountering each other. In spherical powders, this distance is the diameter of the “ball”; in flake powder it is the thickness of the flake; and in multi-perforated extruded powders it is the minimum distance (i.e. wall thickness) between the perforations.
The burning rate of powder composed of grains without any perforations or surface treatment is related to the surface area of the grain available for burning at any given pressure level. The change in the surface area that is burning during combustion is described by a so-called form function. If the surface area increases, the form function does likewise and its behavior is termed progressive. If the form function decreases, its behavior is said to be degressive. If the flame area remains constant throughout the combustion process, we describe it as “neutral” behavior.
The cylindrical, perforated powders are progressive; the burning rate increases as the surface area increases, and the pressure builds up slower, increasing until it reaches its peak and then collapses. Flake and ball grains are degressive; the total powder surface area and pressure are at their peak at ignition, decreasing as the combustion progresses.
This article originally appeared on the Vihtavuori Website.
February 15th, 2024
Story by Boyd Allen
While many top competitive shooters trickle their stick powder charges to a kernel or two, that would be impractical when loading charges for giant naval guns. You may be surprised, but the shells fired by the U.S. Navy’s massive 14″ and 16″ naval guns were also propelled by stick-type extruded powders. You couldn’t trickle these ‘kernels’ though — a single stick or ‘grain’ can be over 2″ long.
The U.S.S. Iowa fires her massive 16″ main battery. The U.S. Navy’s Iowa-class battleships carried nine huge 16-inch Mark 7 cannons in three turrets. The big naval guns were 50 calibers long, i.e. 50 times bore diameter, making the barrels 66.7 feet long from chamber to muzzle. |
In connection with a Benchrest Central discussion that drifted to the subject of powders used in large naval guns, I heard from Joe McNeil, whose father was involved in manufacturing those very propellants as a DuPont employee. Joe writes:
“My Dad worked for the DuPont company for over 40 years. Every time the nation went to war he was assigned to the gun powder plants which DuPont ran for the government for $1.00 per year! His last assignment was at the Indiana Ordnance Plant in Jefferson, Indiana from 1952 through 1958. He had a display case made of all of the different powders made at the plant and left it to me. That’s why I have a grain of 16″ gun powder. He took me out to the Jefferson proving grounds once when they tested the powder in a 16″ gun. We watched from a half-mile away but it left a lasting impression when they fired that gun. They actually had a set of rings they fired through to test the performance of the powder and shell. This was a truly fond memory of my Dad and his work.”
Here are some pictures of the gun powder “grains” made during the Korean War at the Indiana Ordnance Works where Joe McNeil’s father worked.
Above is the display case with the different powders manufactured at the DuPont plant. They include: 37 MM/AA, 75MM Pack Howitzer, 50 Cal. 5010, 20 MM 4831, 30 Cal. 4895, 76 MM, 3″, 5″, 90 MM, 4.7″, 240MM, 8″, 280 MM, 175 MM, 155 MM Howitzer, 155 MM Gun M.P., 8″ Gun M.P., 12″, 14, 16″. There are different-sized ‘grains’ for specific rounds.
16-inch/50-caliber gun projectile plus six propellant bags. Display mockup aboard U.S.S. Iowa (BB-61) in San Pedro, CA. Photo by James Madison per Creative Commons CC-BY-SA-4.0 license.
January 6th, 2024
SUMMARY: Powder can have a very long shelf life. You need to watch for changes in smell and color. A reddish tinge, almost like rust on the powder, is a bad sign, as is a foul odor, not to be confused with a normal chemical smell. Either of these signs indicate it is time to dispose of your powder by means other than shooting.
Ever wondered about the stability of the propellants in your reloading room? There are some important things you should know about powder storage, to ensure consistent powder performance and safety. Western Powders (which has been acquired by Hodgdon) published an informative Q & A series entitled Dear Labby: Questions for our Ballistics Lab . Here are some excerpts that pertain to powder storage and shelf life. Worried that your powder may be too old? Western’s experts explain how to check your propellants for warning signs.
Proper Powder Storage
Q: I live in southern Arizona where it is very hot. I am told powders will become unstable if stored in an area not air-conditioned. My wife says no powder or primers in the house. Can powder be stored in a refrigerator? What about using a fireproof safe? I would appreciate your ideas. — M.C.
Lab Answer: SAAMI guidelines are pretty clear on issues of storage. They recommend storing smokeless powder in containers that will not allow pressure to build if the powder is ignited — ruling out gun safes and refrigerators.
CLICK HERE to Read SAAMI Guidelines for Powder Storage (PDF)
In their original containers, the lifespan of smokeless powders is quite long, even in hot, arid climates. In fact the lifespan is typically longer than the average handloader would need to store them. Stored safely in a garage or outbuilding, your powder should last years. If you see the powder developing a reddish tint, or giving off a foul odor, it is time to discard it.
Clumps in Powder Container
Q: I ordered some of your Accurate 1680 powder back about in December. I just now opened it … and it is full of clumps. My knowledge tells me that means moisture. Am I wrong? I just now broke the seal and it has been stored in a ammo can with desiccant packs around it and a dehumidifier running 14-16 hours a day. I can’t imagine this being my fault, if this does indicate moisture. I don’t know if the pink part on the label is suppose to be red or not, but it is definitely pink, so if it was red I am wondering if I was shipped an old container? I hope that this isn’t bad and I am stuck with it…
Lab Answer: All powder contains a certain amount of moisture. When the powder is stored or during shipping, it can go through temperature cycles. During the cycling, the moisture can be pulled to the surface and cause clumping. Clumping can also be caused by static electricity if too dry or the powder has limited graphite content. You can break up the clumps before metering and they shouldn’t be a problem. This will not affect the powder performance, so your product is fine. Accurate 1680 labels are designed in Pink. As a side note, specification for testing powder is at 70° F and 60% humidity.
Shelf Life and Packaging Dates
Q: Does powder ever get to old to use and what identifying marks does your company put on the canister for when it is made, You have helped me out a while ago when I asked about keeping my cowboy shooting under 950 fps and it works great less stress on the hand and the recoil is very minimum. — R.B.
Lab Answer: On one pound bottles, the number is on the corner in a silver box. If the powder was poured today, it would read 012815 followed by a lot number. The whole number would look something like 012815749. Eight pound bottles have a sticker on the bottom with an obvious date code. The lot number appears above the date.
December 12th, 2022
SUMMARY: Powder can have a very long shelf life. You need to watch for changes in smell and color. A reddish tinge, almost like rust on the powder, is a bad sign, as is a foul odor, not to be confused with a normal chemical smell. Either of these signs indicate it is time to dispose of your powder by means other than shooting.
Ever wondered about the stability of the propellants in your reloading room? There are some important things you should know about powder storage, to ensure consistent powder performance and safety. Western Powders (which has been acquired by Hodgdon) published an informative Q & A series entitled Dear Labby: Questions for our Ballistics Lab . Here are some excerpts that pertain to powder storage and shelf life. Worried that your powder may be too old? Western’s experts explain how to check your propellants for warning signs.
Proper Powder Storage
Q: I live in southern Arizona where it is very hot. I am told powders will become unstable if stored in an area not air-conditioned. My wife says no powder or primers in the house. Can powder be stored in a refrigerator? What about using a fireproof safe? I would appreciate your ideas. — M.C.
Lab Answer: SAAMI guidelines are pretty clear on issues of storage. They recommend storing smokeless powder in containers that will not allow pressure to build if the powder is ignited — ruling out gun safes and refrigerators.
CLICK HERE to Read SAAMI Guidelines for Powder Storage (PDF)
In their original containers, the lifespan of smokeless powders is quite long, even in hot, arid climates. In fact the lifespan is typically longer than the average handloader would need to store them. Stored safely in a garage or outbuilding, your powder should last years. If you see the powder developing a reddish tint, or giving off a foul odor, it is time to discard it.
Clumps in Powder Container
Q: I ordered some of your Accurate 1680 powder back about in December. I just now opened it … and it is full of clumps. My knowledge tells me that means moisture. Am I wrong? I just now broke the seal and it has been stored in a ammo can with desiccant packs around it and a dehumidifier running 14-16 hours a day. I can’t imagine this being my fault, if this does indicate moisture. I don’t know if the pink part on the label is suppose to be red or not, but it is definitely pink, so if it was red I am wondering if I was shipped an old container? I hope that this isn’t bad and I am stuck with it…
Lab Answer: All powder contains a certain amount of moisture. When the powder is stored or during shipping, it can go through temperature cycles. During the cycling, the moisture can be pulled to the surface and cause clumping. Clumping can also be caused by static electricity if too dry or the powder has limited graphite content. You can break up the clumps before metering and they shouldn’t be a problem. This will not affect the powder performance, so your product is fine. Accurate 1680 labels are designed in Pink. As a side note, specification for testing powder is at 70° F and 60% humidity.
Shelf Life and Packaging Dates
Q: Does powder ever get to old to use and what identifying marks does your company put on the canister for when it is made, You have helped me out a while ago when I asked about keeping my cowboy shooting under 950 fps and it works great less stress on the hand and the recoil is very minimum. — R.B.
Lab Answer: On one pound bottles, the number is on the corner in a silver box. If the powder was poured today, it would read 012815 followed by a lot number. The whole number would look something like 012815749. Eight pound bottles have a sticker on the bottom with an obvious date code. The lot number appears above the date.
July 10th, 2022
Story by Boyd Allen
While many top competitive shooters trickle their stick powder charges to a kernel or two, that would be impractical when loading charges for giant naval guns. You may be surprised, but the shells fired by the U.S. Navy’s massive 14″ and 16″ naval guns were also propelled by stick-type extruded powders. You couldn’t trickle these ‘kernels’ though — a single stick or ‘grain’ can be over 2″ long.
The U.S.S. Iowa fires her massive 16″ main battery. The U.S. Navy’s Iowa-class battleships carried nine huge 16-inch Mark 7 cannons in three turrets. The big naval guns were 50 calibers long, i.e. 50 times bore diameter, making the barrels 66.7 feet long from chamber to muzzle. |
In connection with a Benchrest Central discussion that drifted to the subject of powders used in large naval guns, I heard from Joe McNeil, whose father was involved in manufacturing those very propellants as a DuPont employee. Joe writes:
“My Dad worked for the DuPont company for over 40 years. Every time the nation went to war he was assigned to the gun powder plants which DuPont ran for the government for $1.00 per year! His last assignment was at the Indiana Ordnance Plant in Jefferson, Indiana from 1952 through 1958. He had a display case made of all of the different powders made at the plant and left it to me. That’s why I have a grain of 16″ gun powder. He took me out to the Jefferson proving grounds once when they tested the powder in a 16″ gun. We watched from a half-mile away but it left a lasting impression when they fired that gun. They actually had a set of rings they fired through to test the performance of the powder and shell. This was a truly fond memory of my Dad and his work.”
Here are some pictures of the gun powder “grains” made during the Korean War at the Indiana Ordnance Works where Joe McNeil’s father worked.
Above is the display case with the different powders manufactured at the DuPont plant. They include: 37 MM/AA, 75MM Pack Howitzer, 50 Cal. 5010, 20 MM 4831, 30 Cal. 4895, 76 MM, 3″, 5″, 90 MM, 4.7″, 240MM, 8″, 280 MM, 175 MM, 155 MM Howitzer, 155 MM Gun M.P., 8″ Gun M.P., 12″, 14, 16″. There are different-sized ‘grains’ for specific rounds.
16-inch/50-caliber gun projectile plus six propellant bags. Display mockup aboard U.S.S. Iowa (BB-61) in San Pedro, CA. Photo by James Madison per Creative Commons CC-BY-SA-4.0 license.
August 24th, 2021
POWDER GRAIN SHAPES — What You Need to Know
The shape of powder grains has a profound effect on the performance of the powder charge, as it concerns both pressure and velocity. There are multiple powder shapes including flake, ball, and extruded or “stick” (both solid and perforated).
So how does powder grain shape affect pressure and muzzle velocity?
In general, it can be said that powder that burns progressively achieves a desired muzzle velocity at lower maximum pressure than a powder that burns neutrally, not to mention a degressive powder. As grain size increases, the maximum pressure moves towards the muzzle, also increasing muzzle blast. Muzzle velocity and pressure can be adjusted by means of the amount of powder or loading density, i.e. the relationship between the powder mass and the volume available to it. As the loading density increases, maximum pressure grows.
All Vihtavuori reloading powders are of the cylindrical, single-perforated extruded stick type. The differences in burning rate between the powders depend on the size of the grain, the wall thickness of the cylinder, the surface coating and the composition. Cylindrical extruded powders can also have multi-perforated grains. The most common types are the 7- and 19-perforated varieties. A multi-perforated powder grain is naturally of a much larger size than one with a single perforation, and is typically used for large caliber ammunition.
Other types of powder grain shapes include sphere or ball, and flake. The ball grains are typically used in automatic firearms but also in rifles and handguns. The ball grain is less costly to produce, as it is not pressed into shape like cylindrical grains. Flake shaped grains are typically used in shotgun loadings.
Web thickness in gunpowder terminology means the minimum distance that the combustion zones can travel within the powder grain without encountering each other. In spherical powders, this distance is the diameter of the “ball”; in flake powder it is the thickness of the flake; and in multi-perforated extruded powders it is the minimum distance (i.e. wall thickness) between the perforations.
The burning rate of powder composed of grains without any perforations or surface treatment is related to the surface area of the grain available for burning at any given pressure level. The change in the surface area that is burning during combustion is described by a so-called form function. If the surface area increases, the form function does likewise and its behavior is termed progressive. If the form function decreases, its behavior is said to be degressive. If the flame area remains constant throughout the combustion process, we describe it as “neutral” behavior.
The cylindrical, perforated powders are progressive; the burning rate increases as the surface area increases, and the pressure builds up slower, increasing until it reaches its peak and then collapses. Flake and ball grains are degressive; the total powder surface area and pressure are at their peak at ignition, decreasing as the combustion progresses.
This article originally appeared on the Vihtavuori Website.
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