This article comes from the Bryan Litz Ballistics Facebook page. That page offers valuable tips on ballistics, marksmanship, and precision reloading, with updates nearly every day of the year. One recent post relates to velocity changes that can occur when traveling away from home.
Q: Is there a physical reason, other than temperature, why sometimes we see a difference in muzzle velocity when we travel to a different location?
Bryan Litz notes: “One reason we found for this is powder humidity. We put out a video on our YouTube channel called “Powder Humidity / Temperature and Storage”. Watch the video below to learn more specifics about the effects of humidity and temperature changes on your loaded ammunition.
Basically, if you develop a load at home, then travel to a dramatically different environment (drier or wetter), and your ammo isn’t hermetically sealed, it can affect the powder burn rate. This can cause muzzle velocity to change.
Humidity Field Tests with 6.5 Creedmoor and H4350
To learn more about the effects of humidity on velocity and ammo performance, we recommend another article found on the ChronoPlotter.com website. This article begins by reviewing research done by Applied Ballistics, Norma, and Vihtavuori.
Then author Michael Coppola covers his extensive experiments with Hodgdon H4350 powder stored with different relative humidity (RH) levels then loaded in 6.5 Creedmoor rounds. The results were quite dramatic: “At its lowest humidity (14.5% RH), our 41.50 gr H4350 charge clocked in at an average 2,879 fps, peaking at 2,901 fps. Its highest humidity (83.5% RH) saw an average of 2,650 fps with a lowest velocity of 2,635 fps. The entire experiment saw an Extreme Spread of 266 fps. Between the desiccated and 66.5% samples, a 10% change in RH resulted in a velocity change of about 25.6 fps. Above 66.5%, this effect nearly doubled and a 10% change in RH resulted in a change of about 57 fps.
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.
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.
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The leaves are falling, and that means the rainy season will soon begin in many areas of the country. With rain comes increased moisture in the air, i.e. increased humidity. And that, in turn, can affect how your powders perform by altering their burn rates.
Most shooters realize that significant changes in temperature will alter how powders perform. That’s why you want to keep your loaded ammo out of the hot sun, and keep rounds out of a hot chamber until you’re ready to fire. But there are other factors to be considered — HUMIDITY for one. This article explains why and how humidity can affect powder burn rates and performance.
We’ve all heard the old adage: “Keep your powder dry”. Well, tests by Norma have demonstrated that even normal environmental differences in humidity can affect the way powders burn, at least over the long term. In the Norma Reloading Manual, Sven-Eric Johansson, head of ballistics at Nexplo/Bofors, presents a very important discussion of water vapor absorption by powder. Johansson demonstrates that the same powder will burn at different rates depending on water content.
Powders Leave the Factory with 0.5 to 1.0% Water Content
Johansson explains that, as manufactured, most powders contain 0.5 to 1% of water by weight. (The relative humidity is “equilibrated” at 40-50% during the manufacturing process to maintain this 0.5-1% moisture content). Importantly, Johansson notes that powder exposed to moist air for a long time will absorb water, causing it to burn at a slower rate. On the other hand, long-term storage in a very dry environment reduces powder moisture content, so the powder burns at a faster rate. In addition, Johansson found that single-base powders are MORE sensitive to relative humidity than are double-base powders (which contain nitroglycerine).
Tests Show Burn Rates Vary with Water Content
In his review of the Norma Manual, Fred Barker notes: “Johansson gives twelve (eye-opening) plots of the velocities and pressures obtained on firing several popular cartridges with dehydrated, normal and hydrated Norma powders (from #200 to MRP). He also gives results on loaded .30-06 and .38 Special cartridges stored for 663 to 683 days in relative humidities of 20% and 86%. So Johansson’s advice is to keep powders tightly capped in their factory containers, and to minimize their exposure to dry or humid air.”
Confirming Johansson’s findings that storage conditions can alter burn rates, Barker observes: “I have about 10 pounds of WWII 4831 powder that has been stored in dry (about 20% RH) Colorado air for more than 60 years. It now burns about like IMR 3031.”
What does this teach us? First, all powders start out with a small, but chemically important, amount of water content. Second, a powder’s water content can change over time, depending on where and how the powder is stored. Third, the water content of your powder DOES make a difference in how it burns, particularly for single-base powders. For example, over a period of time, a powder used (and then recapped) in the hot, dry Southwest will probably behave differently than the same powder used in the humid Southeast.
Reloaders are advised to keep these things in mind. If you want to maintain your powders’ “as manufactured” burn rate, it is wise to head Johannson’s recommendation to keep your powders tightly capped when you’re not actually dispensing charges and avoid exposing your powder to very dry or very humid conditions. The Norma Reloading Manual is available from MidwayUSA for $24.99.
Real-World Example — “Dry” H4831sc Runs Hotter
Robert Whitley agrees that the burn rate of the powder varies with the humidity it absorbs. Robert writes: “I had an 8-lb. jug of H4831SC I kept in my detached garage (it can be humid there). 43.5-44.0 gr of this was superbly accurate with the 115 Bergers out of my 6mm Super X. I got tired of bringing it in and out of the garage to my house for reloading so I brought and kept the jug in my reloading room (a dehumidified room in my house) and after a few weeks I loaded up 43.5 gr, went to a match and it shot awful. I could not figure out what was going on until I put that load back over the chronograph and figured out it was going a good bit faster than before and the load was out of the “sweet spot” (42.5 – 43.0 gr was the max I could load and keep it accurate when it was stored in less humid air). I put the jug back in the garage for a few weeks and I now am back to loading 43.5 – 44.0 gr and it shoots great again. I have seen this with other powders too.”
If you have two jugs of the same powder, one kept in a room in your house and one somewhere else where it is drier or more humid, don’t expect the two jugs of the same lot of powder to chrono the same with the same charge weights unless and until they are both stored long enough in the same place to equalize again.
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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.
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.
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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.
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.
Share the post "Long-Term Powder Storage — What You Need to Know"
Most shooters realize that significant changes in temperature will alter how powders perform. That’s why you want to keep your loaded ammo out of the hot sun, and keep rounds out of a hot chamber until you’re ready to fire. But there are other factors to be considered — HUMIDITY for one. This article explains why and how humidity can affect powder burn rates and performance.
We’ve all heard the old adage: “Keep your powder dry”. Well, tests by Norma have demonstrated that even normal environmental differences in humidity can affect the way powders burn, at least over the long term. In the Norma Reloading Manual, Sven-Eric Johansson, head of ballistics at Nexplo/Bofors, presents a very important discussion of water vapor absorption by powder. Johansson demonstrates that the same powder will burn at different rates depending on water content.
Powders Leave the Factory with 0.5 to 1.0% Water Content
Johansson explains that, as manufactured, most powders contain 0.5 to 1% of water by weight. (The relative humidity is “equilibrated” at 40-50% during the manufacturing process to maintain this 0.5-1% moisture content). Importantly, Johansson notes that powder exposed to moist air for a long time will absorb water, causing it to burn at a slower rate. On the other hand, long-term storage in a very dry environment reduces powder moisture content, so the powder burns at a faster rate. In addition, Johansson found that single-base powders are MORE sensitive to relative humidity than are double-base powders (which contain nitroglycerine).
Tests Show Burn Rates Vary with Water Content
In his review of the Norma Manual, Fred Barker notes: “Johansson gives twelve (eye-opening) plots of the velocities and pressures obtained on firing several popular cartridges with dehydrated, normal and hydrated Norma powders (from #200 to MRP). He also gives results on loaded .30-06 and .38 Special cartridges stored for 663 to 683 days in relative humidities of 20% and 86%. So Johansson’s advice is to keep powders tightly capped in their factory containers, and to minimize their exposure to dry or humid air.”
Confirming Johansson’s findings that storage conditions can alter burn rates, Barker observes: “I have about 10 pounds of WWII 4831 powder that has been stored in dry (about 20% RH) Colorado air for more than 60 years. It now burns about like IMR 3031.”
What does this teach us? First, all powders start out with a small, but chemically important, amount of water content. Second, a powder’s water content can change over time, depending on where and how the powder is stored. Third, the water content of your powder DOES make a difference in how it burns, particularly for single-base powders. For example, over a period of time, a powder used (and then recapped) in the hot, dry Southwest will probably behave differently than the same powder used in the humid Southeast.
Reloaders are advised to keep these things in mind. If you want to maintain your powders’ “as manufactured” burn rate, it is wise to head Johannson’s recommendation to keep your powders tightly capped when you’re not actually dispensing charges and avoid exposing your powder to very dry or very humid conditions. The Norma Reloading Manual is available from MidwayUSA for $24.99.
Real-World Example — “Dry” H4831sc Runs Hotter
Robert Whitley agrees that the burn rate of the powder varies with the humidity it absorbs. Robert writes: “I had an 8-lb. jug of H4831SC I kept in my detached garage (it can be humid there). 43.5-44.0 gr of this was superbly accurate with the 115 Bergers out of my 6mm Super X. I got tired of bringing it in and out of the garage to my house for reloading so I brought and kept the jug in my reloading room (a dehumidified room in my house) and after a few weeks I loaded up 43.5 gr, went to a match and it shot awful. I could not figure out what was going on until I put that load back over the chronograph and figured out it was going a good bit faster than before and the load was out of the “sweet spot” (42.5 – 43.0 gr was the max I could load and keep it accurate when it was stored in less humid air). I put the jug back in the garage for a few weeks and I now am back to loading 43.5 – 44.0 gr and it shoots great again. I have seen this with other powders too.”
If you have two jugs of the same powder, one kept in a room in your house and one somewhere else where it is drier or more humid, don’t expect the two jugs of the same lot of powder to chrono the same with the same charge weights unless and until they are both stored long enough in the same place to equalize again.
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Here’s a smart new product that monitors the temperature and humidity inside your gun safe — with a convenient LCD display unit located on the outside of the safe. You don’t need to string wires or cut a small hole in your safe — there are two separate components, one inside and one outside. The sensor unit (on the inside) communicates wirelessly with the display unit (on the outside).
The new GoldenRod Wireless Hygrometer was designed to display the temp/humidity in your safe without the need to open the safe. NOTE: the wireless LCD display can show BOTH in-vault AND in-room humidity and temperature levels. You can attach the display to the vault door with its built-in magnet, or simply place the display unit on top of the safe using the handy flip-out kickstand. The unit costs just $26.98 at Amazon.com.
GoldenRod Wireless Hygrometer Specifications and Features:
Measures In-Vault and In-Room humidity from 20% to 95%.
Measures In-Vault temperature range from 14°F to 122°F.
Measures In-Room temperature range from -4°F to 158°F.
Records Min/Max temperature and humidity history.
Another Important Accessory — GoldenRod for Inside the Safe
The GoldenRod, marketed as a dehumidifier, is a small, low-wattage electric heating element you place in the safe. Running 24/7 at 140° F, the GoldenRod warms the air in your safe. This changes relative humidity and raises the dew point in the safe so water vapor does not condense on your arms and valuable accessories. When combined with Desiccant packs that absorb moisture, the GoldenRod is extremely effective at keeping your guns rust-free during long-term storage. We do recommend wiping down your guns with Boeshield, Eezox, or Corrosion-X before putting them in storage. These are three of the best corrosion-inhibiting metal coatings you can buy.
You can get the 12″ GoldenRod heating unit for $31.99 on Amazon. There is also an 18″ model for $48.75 and a long 36″ GoldenRod for $39.99 on Amazon, just $8 more than the “foot-long”. The 36″ GoldenRod works well for cold climates and large safes. All GoldenRods come with a detachable plugs for easy installation. The 12″ is rated for 100 cubic foot safes, the 18″ for 200 cubic foot safes, while the 36″ model protects up to 500 cubic feet.
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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. On its website, Western Powders (vendors of Accurate, Norma, and Ramshot powders) 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.
In their original containers smokeless powder’s lifespan is quite long, even in your hot, arid climate, 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.
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Powder Moisture Content — Did You Know?
Variations in moisture content change the burning rate of a powder and thereby chamber pressures and muzzle velocity. The moisture content of the Vihtavuori N100 and N300 series powders is usually around 1%, while the N500-series’ normal moisture content is 0.6% because of the added nitroglycerine.
So what difference does moisture content make? Here’s an example. In a test, a [Vihtavuori] powder sample was dried by heating it, losing about 0.5 % of its weight. Cartridges were then loaded with the dried powder and fired using a pressure gun. Chamber pressures and muzzle velocities produced by these special cartridges were compared to those produced by cartridges loaded with untreated powder. (The powder charge and bullet were of course the same in both sets of cartridges.)
After Powder Drying:
Pressure Increased 11% from 320 MPa to 355 MPa
Velocity Increased 2.6% from 2526 to 2592 FPS
Comparing results showed chamber pressures increased from 320 MPa to 355 MPa with the dried powder, and the muzzle velocity increased accordingly from 770 m/s to 790 m/s (2526 to 2592 FPS). And note, this is only one example, of one caliber and loading. The difference might be much higher depending on the cartridge and loading combinations.
Recommendation: Store powder below 68°F in 55-65% humidity.
What does this tell us? Well, it seems we need to forget the old saying “Keep your powder dry”! Instead, focus on proper powder storage, at a temperature below 20°C/68°F and humidity between 55 and 65%. Safe reloading everybody!
Tech Tip sourced by EdLongrange. We welcome reader submissions.
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Most shooters realize that significant changes in temperature will alter how powders perform. That’s why you want to keep your loaded ammo out of the hot sun, and keep rounds out of a hot chamber until you’re ready to fire. But there are other factors to be considered — HUMIDITY for one. This article explains why and how humidity can affect powder burn rates and performance.
We’ve all heard the old adage: “Keep your powder dry”. Well, tests by Norma have demonstrated that even normal environmental differences in humidity can affect the way powders burn, at least over the long term. In the Norma Reloading Manual, Sven-Eric Johansson, head of ballistics at Nexplo/Bofors, presents a very important discussion of water vapor absorption by powder. Johansson demonstrates that the same powder will burn at different rates depending on water content.
Powders Leave the Factory with 0.5 to 1.0% Water Content
Johansson explains that, as manufactured, most powders contain 0.5 to 1% of water by weight. (The relative humidity is “equilibrated” at 40-50% during the manufacturing process to maintain this 0.5-1% moisture content). Importantly, Johansson notes that powder exposed to moist air for a long time will absorb water, causing it to burn at a slower rate. On the other hand, long-term storage in a very dry environment reduces powder moisture content, so the powder burns at a faster rate. In addition, Johansson found that single-base powders are MORE sensitive to relative humidity than are double-base powders (which contain nitroglycerine).
Tests Show Burn Rates Vary with Water Content
In his review of the Norma Manual, Fred Barker notes: “Johansson gives twelve (eye-opening) plots of the velocities and pressures obtained on firing several popular cartridges with dehydrated, normal and hydrated Norma powders (from #200 to MRP). He also gives results on loaded .30-06 and .38 Special cartridges stored for 663 to 683 days in relative humidities of 20% and 86%. So Johansson’s advice is to keep powders tightly capped in their factory containers, and to minimize their exposure to dry or humid air.”
Confirming Johansson’s findings that storage conditions can alter burn rates, Barker observes: “I have about 10 pounds of WWII 4831 powder that has been stored in dry (about 20% RH) Colorado air for more than 60 years. It now burns about like IMR 3031.”
What does this teach us? First, all powders start out with a small, but chemically important, amount of water content. Second, a powder’s water content can change over time, depending on where and how the powder is stored. Third, the water content of your powder DOES make a difference in how it burns, particularly for single-base powders. For example, over a period of time, a powder used (and then recapped) in the hot, dry Southwest will probably behave differently than the same powder used in the humid Southeast.
Reloaders are advised to keep these things in mind. If you want to maintain your powders’ “as manufactured” burn rate, it is wise to head Johannson’s recommendation to keep your powders tightly capped when you’re not actually dispensing charges and avoid exposing your powder to very dry or very humid conditions. The Norma Reloading Manual is available from Amazon.com.
Real-World Example — “Dry” H4831sc Runs Hotter
Robert Whitley agrees that the burn rate of the powder varies with the humidity it absorbs. Robert writes: “I had an 8-lb. jug of H4831SC I kept in my detached garage (it can be humid there). 43.5-44.0 gr of this was superbly accurate with the 115 Bergers out of my 6mm Super X. I got tired of bringing it in and out of the garage to my house for reloading so I brought and kept the jug in my reloading room (a dehumidified room in my house) and after a few weeks I loaded up 43.5 gr, went to a match and it shot awful. I could not figure out what was going on until I put that load back over the chronograph and figured out it was going a good bit faster than before and the load was out of the “sweet spot” (42.5 – 43.0 gr was the max I could load and keep it accurate when it was stored in less humid air). I put the jug back in the garage for a few weeks and I now am back to loading 43.5 – 44.0 gr and it shoots great again. I have seen this with other powders too.”
If you have two jugs of the same powder, one kept in a room in your house and one somewhere else where it is drier or more humid, don’t expect the two jugs of the same lot of powder to chrono the same with the same charge weights unless and until they are both stored long enough in the same place to equalize again.
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In this video, Bryan Litz of Applied Ballistics talks about Density Altitude and the effect of atmospheric conditions on bullet flight. Bryan explains why you must accurately account for Density Altitude when figuring long-range trajectories.
Bryan tells us: “One of the important elements in calculating a fire solution for long-range shooting is understanding the effect of atmospherics. Temperature, pressure, and humidity all affect the air density that the bullet’s flying through. You can combine all those effects into one number (value) called ‘Density Altitude’. That means that you just have one number to track instead of three. But, ultimately, what you are doing is that you are describing to your ballistics solver the characteristics of the atmosphere that your bullet’s flying through so that the software can make the necessary adjustments and account for it in its calculations for drop and wind drift.”
Bryan adds: “Once you get past 500 or 600 yards you really need to start paying careful attention to atmospherics and account for them in your ballistic solutions”. You can learn more about Density Altitude in Bryan’s book, Applied Ballistics for Long Range Shooting (Third Edition).
General Scientific Definition of Density Altitude
Density altitude is the altitude relative to the standard atmosphere conditions (ISA) at which the air density would be equal to the indicated air density at the place of observation. Density altitude can be calculated from atmospheric pressure and temperature (assuming dry air). Here is the formula:
Air is more dense at lower elevations primarily because of gravity: “As gravity pulls the air towards the ground, [lower] molecules are subject to the additional weight of all the molecules above. This additional weight means the air pressure is highest at sea level, and diminishes with increases in elevation”.*
Both an increase in temperature, decrease in atmospheric pressure, and, to a much lesser degree, increase in humidity will cause an increase in density altitude. In hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.
We’ve all heard the old adage: “Keep your powder dry.” Well, tests by Norma have demonstrated that even normal environmental differences in humidity can affect the way powders burn, at least over the long term. In the Norma Reloading Manual, Sven-Eric Johansson, head of ballistics at Nexplo/Bofors, presents a very important discussion of water vapor absorption by powder. Johansson demonstrates that the same powder will burn at different rates depending on water content.
Powders Leave the Factory with 0.5 to 1.0% Water Content
Johansson explains that, as manufactured, most powders contain 0.5 to 1% of water by weight. (The relative humidity is “equilibrated” at 40-50% during the manufacturing process to maintain this 0.5-1% moisture content). Importantly, Johansson notes that powder exposed to moist air for a long time will absorb water, causing it to burn at a slower rate. On the other hand, long-term storage in a very dry environment reduces powder moisture content, so the powder burns at a faster rate. In addition, Johansson found that single-base powders are MORE sensitive to relative humidity than are double-base powders (which contain nitroglycerine).
Tests Show Burn Rates Vary with Water Content
In his review of the Norma Manual, Fred Barker notes: “Johansson gives twelve (eye-opening) plots of the velocities and pressures obtained on firing several popular cartridges with dehydrated, normal and hydrated Norma powders (from #200 to MRP). He also gives results on loaded .30-06 and .38 Special cartridges stored for 663 to 683 days in relative humidities of 20% and 86%. So Johansson’s advice is to keep powders tightly capped in their factory containers, and to minimize their exposure to dry or humid air.”
Confirming Johansson’s findings that storage conditions can alter burn rates, Barker observes: “I have about 10 pounds of WWII 4831 powder that has been stored in dry (about 20% RH) Colorado air for more than 60 years. It now burns about like IMR 3031.”
What does this teach us? First, all powders start out with a small, but chemically important, amount of water content. Second, a powder’s water content can change over time, depending on where and how the powder is stored. Third, the water content of your powder DOES make a difference in how it burns, particularly for single-base powders. For example, over a period of time, a powder used (and then recapped) in the hot, dry Southwest will probably behave differently than the same powder used in the humid Southeast.
Reloaders are advised to keep these things in mind. If you want to maintain your powders’ “as manufactured” burn rate, it is wise to head Johannson’s recommendation to keep your powders tightly capped when you’re not actually dispensing charges and avoid exposing your powder to very dry or very humid conditions. The Norma Reloading Manual is available from Amazon.com.
Real-World Example — “Dry” H4831sc Runs Hotter
Robert Whitley agrees that the burn rate of the powder varies with the humidity it absorbs. Robert writes: “I had an 8-lb. jug of H4831SC I kept in my detached garage (it can be humid there). 43.5-44.0 gr of this was superbly accurate with the 115 Bergers out of my 6mm Super X. I got tired of bringing it in and out of the garage to my house for reloading so I brought and kept the jug in my reloading room (a dehumidified room in my house) and after a few weeks I loaded up 43.5 gr, went to a match and it shot awful. I could not figure out what was going on until I put that load back over the chronograph and figured out it was going a good bit faster than before and the load was out of the “sweet spot” (42.5 – 43.0 gr was the max I could load and keep it accurate when it was stored in less humid air). I put the jug back in the garage for a few weeks and I now am back to loading 43.5 – 44.0 gr and it shoots great again. I have seen this with other powders too.”
If you have two jugs of the same powder, one kept in a room in your house and one somewhere else where it is drier or more humid, don’t expect the two jugs of the same lot of powder to chrono the same with the same charge weights unless and until they are both stored long enough in the same place to equalize again.
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Tests Show Burn Rates Vary with Water Content
Here’s a smart new product that monitors the temperature and humidity inside your gun safe — with a convenient LCD display unit located on the outside of the safe. You don’t need to string wires or cut a small hole in your safe — there are two separate components, one inside and one outside. The sensor unit (on the inside) communicates wirelessly with the display unit (on the outside).
