Powder overall weight/power.

Blindstitch · May 10, 2013, 07:10 PM

I have an odd curiosity question.

Can the weight of a powder change? I know it's a dry good but say we measure two containers of 500 grains of powder out. Then place one in a warmer sunny environment for some time and another in a heat controlled area at 68 degrees.

Will the hot climate one weight less and have any more power than the other?

I saw a video saying that if you are shooting on a hot day and leave your ammo in the sun it will heat up and but will also shoot like a hotter load.

SL1 · May 10, 2013, 07:38 PM

You are confusing two factors.

First, yes, powdeer cah change weight. Not by much, but it is measureable. Mainly by absorbing water, but also by losing some of the volatile solvents that remain in the formulation (which is what you smell with single-based powders). So, powder that is stored where it can get damp will weigh more per unit volume as it absorbs some water.

But, that is not what is involved with leaving cartridges in the sun. The powder sealed in the cartridge does not change its energy content, and really can't change its weight by much because it is pretty much sealed in.

What does happen is that the powder burns "faster" when it is started at a higher temperature, liberating the energy faster so that the PEAK pressure is higher.

Why this happens is somewhat complicated to explain, and may have something to do with ignition speed from the primer as well as burning speed once the powder is ignited. Smokeless powder burns at a faster rate as the pressure is increased, so what happens in a cartridge is a balance between the powder buring speed accelerating due to the gas it produces increasing pressure, while the bullet starting to move down the bore is tending to reduce pressure by letting the gases expand.

Some powders have been specially formulated to reduce their sensitivity to the temperature at which they are fired, but that process is proprietary and not something I could explain if I understood it myself.

SL1

May 10, 2013, 07:10 PM	#1
Blindstitch Senior Member Join Date: April 14, 2013 Location: Milwaukee, Wisconsin Posts: 2,693	Powder overall weight/power. I have an odd curiosity question. Can the weight of a powder change? I know it's a dry good but say we measure two containers of 500 grains of powder out. Then place one in a warmer sunny environment for some time and another in a heat controlled area at 68 degrees. Will the hot climate one weight less and have any more power than the other? I saw a video saying that if you are shooting on a hot day and leave your ammo in the sun it will heat up and but will also shoot like a hotter load.

May 10, 2013, 07:38 PM	#2
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	You are confusing two factors. First, yes, powdeer cah change weight. Not by much, but it is measureable. Mainly by absorbing water, but also by losing some of the volatile solvents that remain in the formulation (which is what you smell with single-based powders). So, powder that is stored where it can get damp will weigh more per unit volume as it absorbs some water. But, that is not what is involved with leaving cartridges in the sun. The powder sealed in the cartridge does not change its energy content, and really can't change its weight by much because it is pretty much sealed in. What does happen is that the powder burns "faster" when it is started at a higher temperature, liberating the energy faster so that the PEAK pressure is higher. Why this happens is somewhat complicated to explain, and may have something to do with ignition speed from the primer as well as burning speed once the powder is ignited. Smokeless powder burns at a faster rate as the pressure is increased, so what happens in a cartridge is a balance between the powder buring speed accelerating due to the gas it produces increasing pressure, while the bullet starting to move down the bore is tending to reduce pressure by letting the gases expand. Some powders have been specially formulated to reduce their sensitivity to the temperature at which they are fired, but that process is proprietary and not something I could explain if I understood it myself. SL1