I had a very interesting thing happen to me just this past week. As I was running out of one 8 lb jug of H4350 I started to think about opening my new jug and get things back on track. I shoot a very accurate 6.5x47 Lapua with 130 gr Berger VLD's, Lapua cases and CCI 450 sm rifle mag primers. My nominal vel is 2800 fps with the old powder. This rifle/load combo always gives me single digit SD's and sub .7 MOA accuracy on a "bad" day. It usually runs sub .4 MOA; always 5-shots. I have an acquaintance who works as a ballistic lab tech for ADI (Australian Defense Industries), they make most of Hodgdon powders. I emailed him to see about how different the two lots of H4350 would be. I gave him the lot #'s and he said I would need to add about .3 gr of powder to equal my nominal 2800 fps with the old 8 lb jug of H4350. I opened the new jug and poured off about a 1/2 lb of powder directly into my Harrell's Premium powder meter and started thowing then weighing 40.8 gr of the fresh jug of H4350. My standard tolerance when I weigh for this rifle is +/- .002 gr. Yes, four one hundred's of a grain. I can do that with my VIC 123 elec scale.

So, Saturday morning, I go to the range and shoot some 100 yd, 5-shot groups and they open up to 1.125" and have an SD of 24.5 which is horrible for this rifle. Also, my velocity for the 40.8 gr is 2804 fps, right where I hope it to be. I like the velocity but not the group nor ES/SD. I email him about the results to see if he has an insight on what might have happened. Before he has a chance to reply I figure I just need to run a smallish ladder to find the sweet spot node again. I load up 6 different charges in .2 gr increments; 40 to 41 gr. I go to the range yesterday am and shoot at 360 yds. Marking each ogive with a different color marker so I can tell which bullet powder creates which bullet hole on the paper. Here is a sample.


From what I could see through my 45x Zeiss, things were getting crowded and I didn't want to ruin the entire test, I used a different aim point for the last two
groups and was able to somewhat finish the test. I had logged each and every shots velocity and ES along with average of each 3-shot group. It wasn't until I got home that I noticed the average velocities.

the 40.8 gr average vel was 2886 fps. Just 2 days earlier, the same 40.8 gr charge gave me a 2804 average. Conditions were basically the same, same chrono, etc, yet 82 fps faster. I sent the results off to my associate in Australia. It was enough that he called me to discuss the situation.

What he told me, after asking all kinds of questions to make sure the tests were similar, was that the powder from the freshly opened 8 lb jug had accumulated most of it's .8% moisture in the top of the unopened jug during packaging, shipping and storage. After the first test, I had "tossed' the jug around a bit more and distributed the moisture a bit. At first, I was really confused because to me, the term "moisture" and "powder" don't mix be he told that water is used during one part of the manufacturing process. At least that's what I think I understood at the time as it was a bad connection and things here at my house were getting hectic with my 12 yr old son hollering at me that "mom needed my help".

The first 1/2 lb of powder weighed more per identical volume than when I loaded the same charges 2 days later. Same weight but different volume. Not enough to see when looking down into the case but still different. This made sense to me because if you've ever read Glen Zediker's "Handloading for Competition" you'll know that he dedicates quite a bit to this topic about weighing vs throwing. Basically if you weigh one day and get volume A and weigh another day, getting the same weight, volume B can be different.

So, when you open up a fresh jug of powder, you might consider "tossing" it around to distribute the moisture in the powder so you don't get a significant increase in velocity from your loads. Also, keep your powder lids tight to avoid significant moisture loss. Something else I do to help avoid moisture loss. For every 8-lb jug of powder I own, and it's many different types, I try and keep a 1-lb can available. I pour off enough from the 8-lb jug into the 1-lb can to fill it up. Then when I go to load up a batch of ammo, whether it's 8, 80 or 800 rounds, I use the powder that is in the 1-lb can before opening the 8-lb jug again. That way, I only need to open the 8-lb jug about 7-8 times in the life of the jug before it's all gone; less chance of loosing moisture and changing the ballistics during the life of the 8-lb jug.

Have I thoroughly lost you? Me too! it takes a bit to get your brain wrapped around this topic.

Alan

You may or may not (more than likely not) "lose" moisture by opening the jug. Powder is somewhat hydroscopic (attracts moisture from the air) so when the ambient air humidity is on the high side open powder jugs are sucking moisture FROM the air.

Nonetheless, what you have to say about the moisture content of powder is quite true, although it is best thought of in another way: To the extent that moisture content varies, XX grains of powder with higher moisture has less combustable chemical than XX grains of "drier" powder does.

For purposes of illustration, let's assume that the specific gravity of your powder is exactly 1, the same as water. If your charge is 50 grains and your moisture content is 2%, then you have 49 grains of propellant and one grain of water in your load. If your moisture content is only 1/2%, then you have 49.75 grains of powder and .25 grains of water in your load, or an additional 3/4 grain of powder. Discounting whatever small effect the water itself has on the performance of the powder, you still have an effective increase of 3/4 grain, or about 1.5% in your powder charge between the "wet" powder and the "dry" powder. Since velocity is typically fairly linear in relation to the powder charge (while pressure typically rises at double the rate of velocity), the "dry" powder charge should increase a 3,000 fps load by about 46 fps.

All of this goes to show that you can have a "bad powder day" just like you can have a "bad hair day", depending on how the weather is affecting you.

usually by the time i've dropped it on the floor, spilled half of it all over the loading bench and then picked it back up (less the half pound that's still all over) i figure its been shaken enuf

I am interested in this moisture issue. I reload in my furnace room, where the temps are usually warm and it is drier than the rest of my basement. I store powder in a different, cooler room. I have weighed out charges before and left them set on my reloading bench and come back a couple days later to find them all .2 to .3 grains lighter than what I originally weighed them to. I figure its from moisture loss, should I add additional powder to get them where they should be weight wise, or is it better to leave them light, with the same volume of powder I originally measured?

Also if I leave powder in that warm/dry room for a few days, in my thrower. Will the increased volume, needed to weigh what I want it to, create excessive pressure and be dangerous?

I have enough 1 lb cans from previous use of a particular powder so that when I open a 8 lb jug I fill and seal it all in the 1 lb cans. I fill them to the top so only get about 5 but the cans are full. Then the powder is decanted into the powder measure for loading and returned to the can for storage. I think I have minimum to zero mnoisture up-take or evoration doint it this way.

Von Gruff.