Friends,
Here is some info for all. It will serve as a reminder for some, and probably new for others, but regardless it is good to touch base on.
The short version is that I have a Dillon 550 mounted on a portable table that I put in an enclosed trailer to take to the range to do development work. Recently I got busy and completely forgot to bring it inside at the end of the day. The weather recently had changed, with freezing temps at night/early morning and mid 40s during the day. I then realized my mistake and grabbed the press and brought it in.
Just like when you leave any metal item outside in colder weather and bring it in, it can and will be cold to the touch and gather moisture. Not a huge deal for the most part as the press just needs to warm up and dry out which it will over the course of 24 hours or so, but here is the lesson, reminder.
The powder is the issue.
Fortunately, when doing this type of mobile development, I don't put much powder in the powder measure, so it is not a major thing, one way or another.
I knew that I would get a "wrong" reading when I dropped a powder charge, so I took some pics, and here were the results.
I am not going to discuss what cartridge this is for or the brand/type of powder as this was for T&E purposes, but here are some pics.
The charge was 16.4 grains and dropped extremely consistently.
After being out in overnight freezing temperatures, the powder charge was now a consistent 17.3 grains.
Here is the reminder/lesson.
Powder is hygroscopic. In other words, it absorbs moisture. The minute you open a powder container, it will start to absorb moisture. In the case of being left in a trailer overnight, you have a significant change that is easily verifiable.
The solution of course was simple. In my case, since I only put small amounts of powder in the machine, I simply dumped it. Once the machine was back at room temps, I also disassemble the powder measure, pulling the powder funnel and as a regular part of my cleaning process I wiped everything down with 99% isopropyl alcohol:
Back to the powder. Modern smokeless powder is hygroscopic.
Without going down rabbit holes, the short version is that the higher humidity of your environment, the more moisture your powder is going to absorb. The more controlled you keep your loading environment, the better.
Along these lines, I was recently up at my elderly fathers house. He has a press set up in his shop. He lives in the mountains of central Idaho. His shop is heated only by a wood stove and the temps swings are considerable. He had a bunch of powder in his press and once I got his press tuned and running right, I asked him how long the powder had been there. He did not know. I asked him if it had been over a month. The punch line is that it was probably in there at least 6 months or more, so I dumped it and reminded him to use smaller amounts and why. He is in his 80s and has some age related memory issues, so this is a something that is an ongoing thing.
How does all this affect things? This is something that I learned in my 20s. I was loading for my rifle and left powder in my powder drop for a long period of time. I could not figure out why, while using the same charge, my velocities were so low. Simply put, the more moisture in a powder, the slower your velocity will be, when equal weights are used. It took a while to figure it out, as the access to quality information is not there like we have today thanks to the world wide internet.
Anyways,
Now that my portable mounted 550 has been acclimated back to its regular environment and cleaned, I ran some test drops. It was dropping charges right on the money again, with no adjustments needed.
Anyways, hope this serves as a reminder to some and is educational to others.
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Originally Posted by BN
