A couple of days ago I tested some loads using IMR8028XBR and recorded the velocities. The temperature at the time was in the mid 90's but the humidity wasn't too high. When I tried to repeat the test to-day using the same components I found that the velocities were 100fps slower. The temperature was almost twenty degrees cooler but the humidity was very high and my glasses kept fogging up. Since this powder is supposed to temperature stable I was wondering if the humidity had something to do with it.
Well, every ballistic program I know takes it into account, and water does weigh something, so I would guess that to be a "Yes". How how much, don't know.
Berger makes a ballistic program you can download for free, so search for it and insert some numbers.
Larry
Tinkerer
Yes....affects the burn rate of the powder as well.
High humidity = "heavy air"
I would think air density would affect bullet speed, and besides the difference in humidity, 20 degrees temperature difference is
significant. I copied this out of wikipedia, "Air density decreases with increasing altitude, as does air pressure. It also changes with variances in temperature or humidity." You can try to test your ammo again with similar temp/humidity to the first day and see
if you get that 100fps back.
Based on information from the Hornady site, http://www.hornady.com/ballistics-resource/external, it appears that higher temperatures
do result in higher velocities, and thus lower temperatures in lower velocities. The hornady ballistics resource is an interesting read for those wanting more details.
The way I understood it was that the higher the humidity the faster the bullet goes the atmosphere.
Because the hydrogen molecules are less dense than the oxygen molecules.
I think I read it at Barnes University.
The hotter it is the more pressure you get with the same components and rifle.
The higher the humidity, the closer you are to shooting under water.
Originally Posted by Eric in NC
;D
I like that!
Here in Louisiana you'ld think we need scuba gear to shoot on occasions!
Cool dry air weighs more than warm moist air.
Yes but cool moist air weighs even more!Cool dry air weighs more than warm moist air.
Here is an excerpt from an article written by Dan Lilja:
Contrary to popular opinion, an increase in the humidity level actually decreases the air density. That sticky, humid air is not really "heavy" air after all. Hard to believe? It is true and the reason is that the molecular weight of dry air is greater than that of water. This information can be found in the CRC HANDBOOK OF CHEMISTRY AND PHYSICS. The book is not hard to find, my small town library has it. There is also a brief explanation of this in the exterior ballistics section of the third edition of the Sierra reloading manual. As we will see later though, of all the air density components, a change in the humidity level has the least effect.
If you want to read more, here is the link: http://www.riflebarrels.com/articles...e_humidity.htm
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