Comments on: TECH TIP: Humidity Can Change Powder Burn Rates

By: Bryan Zolnikov

Bryan Zolnikov — Tue, 18 Apr 2023 01:43:50 +0000

In modern HDPE powder jugs, humidity does not penetrate the jug when you close the lid. I have 1.5 years of data showing this. I’ve put this jug in the test outside in 100% humidity for several days and over 70% for months and no change was shown in the humidity in the jug for over 1.5 years.

https://youtu.be/0Shiy0diV4k

By: Dave

Dave — Sat, 16 Jul 2022 21:20:32 +0000

Here is a great article on the topic of how humidity affects powder. I recommend it!

https://chronoplotter.com/2021/08/19/how-does-humidity-affect-powder/

By: Dave

Dave — Sat, 16 Jul 2022 20:07:47 +0000

To try to quantify the FPS changes; I shoot H4350 in my precision 6.5 Creedmoor. I moved from San Diego, CA (dry desert near the ocean) to Middle Tennessee (humid!). My tightly closed 8# jug was kept in a weatherproof tub in the attached garage to avoid air and moisture exchange and reduce the impact of humidity on the powder. I was working up a long range (750 – 1,250 yard) load, at the higher end of the velocity range. Suddenly, there was a 30 FPS drop in muzzle speed. The next time I tried the same recipe, it was a 50 FPS drop. Needless to say, consistency and expected Point-of-Impact have gone down the toilet. I’ve moved the powder jug to a bedroom in the house, but I still have to do my loading in the garage. Frankly, I’m unsure of how to get and keep the powder remaining in the 8# jug to a consistent state so I can find the powder drop that will get the preferred muzzle velocity. Any guidance would be appreciated!

By: Josh

Josh — Tue, 16 Sep 2008 16:10:12 +0000

You might also mention that, over time (weeks to months), the polyethylene bottles provided by powder suppliers are NOT a moisture barrier. It happens slowly, but water vapor does pass right through them.

By: Pao

Pao — Thu, 11 Sep 2008 16:02:16 +0000

So…name some two base powders and which ones are least sensitive to temp.

By: Robert Whitley

Robert Whitley — Wed, 10 Sep 2008 20:30:32 +0000

Great bulletin item – right on the money!

I absolutely agree that the burn rate of the powder varies with the humidity it absorbs. For example, I had an 8lb jug of H4831SC I kept in my detached garage (it’s somewhat humid there). 43.5-44 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 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 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 – been there – done that!

Robert Whitley