Overgassing in hot weather temperatures?

[lysander]

Which powders are more stable? I've always thought of XBR as one of the best off the shelf options commonly available. (Not that it's common anymore.)

The lower the number the less change in velocity per degree change in temperature, i.e., the lower the better.

[mRad]

Which powders are more stable? I've always thought of XBR as one of the best off the shelf options commonly available. (Not that it's common anymore.)

In my experience from using them, Varget, H4350, H4831SC, H1000, etc. basically every powder in the Extreme line of powders is as good as you can get.


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[T2C]

Good information Lysander. From this point forward I am going to take a surface thermometer, in addition to a regular thermometer, with me to the range when I collect data.

[mRad]

Good information Lysander. From this point forward I am going to take a surface thermometer, in addition to a regular thermometer, with me to the range when I collect data.

One thing you can do to experiment is take a cooler on a hot day. Also be sure not to let a round bake in the chamber of a hot barrel.


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[lysander]

Good information Lysander. From this point forward I am going to take a surface thermometer, in addition to a regular thermometer, with me to the range when I collect data.

The artillery guys always had a little thermometer in with the propelling charges. The fire direction center would use that information to fine tune the firing elevation.

There is also a misconception that the barrel temperature is the only important factor, or that hot ammunition in a cold barrel will not be effected.

When propellant burns, it releases energy inside the grains of powder, if the grains are hot, they have, in addition to the stored chemical energy, thermal energy. So, hot propellant will produce higher pressures and velocities.

A hot barrel may warp, or droop, or may experience some other phenomenon that changes the point of impact or accuracy, as well.

[mRad]

The artillery guys always had a little thermometer in with the propelling charges. The fire direction center would use that information to fine tune the firing elevation.

There is also a misconception that the barrel temperature is the only important factor, or that hot ammunition in a cold barrel will not be effected.

When propellant burns, it releases energy inside the grains of powder, if the grains are hot, they have, in addition to the stored chemical energy, thermal energy. So, hot propellant will produce higher pressures and velocities.

A hot barrel may warp, or droop, or may experience some other phenomenon that changes the point of impact or accuracy, as well.

Good description. I would add that with small arms, as the barrel heats and molecules expand, the bore is tighter and created more pressure and thus the increased velocity is amplified.

When testing ammunition, the time between shots needs to allow the bore to cool. When testing barrels, it’s good to know what it and the ammunition does with increased rate of fire.


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