Humidity effect on powder charge weight

[boiler_house7]

Well I guess you could say I live in a somewhat very dry climate 20% humidity on the average. luckily we have been blessed with several day's of rain. I have noticed my powder dump drop charge has increased a couple of tenths when weighting my powder on the same dump setting. It has always been close to a 1/10 low and I finish with a trickle. is it common to see the humidity affect powder weight this much. Thanks Bill

 

[SDDasher]

OK I will jump in on this one. I live in a humid environment averageing about 80-90% this time of the year. We call it air you can wear.On those rare days with; lower humidity I too notice a greater variance
in scale "drift". To help solve the issue I use a spray static guard. Works great according to my chrono results with consistent velocity and low SD&ES.

 

[BoydAllen]

I don't think that the OP is talking about and erratic scale, but rather that it seemed to him that a given volume of powder weighed more, by a couple of tenths. Recently there has been some experimentation along those lines, and it seemed to indicate that when powder contains more moisture, that its burn rate, and the velocity it produces are reduced. The tests were done with some care, and an article published in Precision Shooting Magazine some time back.

 

[boiler_house7]

Thanks boyd , I would like to find that article. I had left some powder in my powder dump and we got some good rains for a few days. I went to load up a few rounds and noticed this difference. I put the powder back in my jug and gave it a shake and put the powder back in the dump and my setting was back close to normal. I will from now on always put my powder back in the jug after loading, it seems to me like you mentioned if I would have loaded you would think I would have been a little low on actual velocity, dunno, makes sense when you got a fairly tight window on your node. Thanks Bill

 

[THOMAST]

I have a digital hygrometer in my reloading room to keep an eye on the humidity level.A heater/fan helps to lower humidity when it gets too humid. I like to work at 60% humidity level when dispensing propellant.

 

[82boy]

is it common to see the humidity affect powder weight this much. Thanks Bill

Yes, This is why competitive Benchrest shooters will weigh charges and keep an eye on this throughout the day. First thing in the morning it is not uncommon for Benchrest shooters will take several different charges to the line, usually they take what was working before, a charge lighter, and a charge heavier. They will find a base line, and change from there as they day and humidity and temperature change. The better shooters know the ins and outs with a certain type of powder, and know what it does as the day goes one, and humidity and temperature changes. It is also not uncommon for them to use different powders for different climates, such as n133 on damp cold days, 8208 on hot dry days, and so on. The main thing is to learn your powder, and know what it does in different situations.

 

[BoydAllen]

A little added note on weighing at the range, something that has recently occurred to me, if powder gets heavier and slower as it gains moisture, which tests show that it does, then while weighing charges at the range may give superior charge uniformity within a group, it may also exaggerate the changes caused by powder gaining or loosing moisture. For instance, if powder drys throughout the day. More granules will be in a given weight charge toward the end, and they will be faster. The reverse being true if the powder is gaining moisture. On the other hand, given that short range benchrest is less sensitive to ES than longer range competitions, if charges are thrown as well as they can be, a given measure setting may produce heavier charges (as mentioned by the previous poster) as the powder gains moisture, which would help to compensate for its reduction in burn rate. The newest powder in the short range benchrest world LT32 powder. Its shape makes it much easier to throw than the previously dominant powder, VV 133. For that reason shooters may not need to weigh it to have satisfactorily uniform charges, and there may actually be a small advantage in thrown charges, if technique is good, given what I mentioned above.