Power, temp sensitivity, and throw size

[Alan Adamson]

All,

So a thread about Silhouette and it's potential reverse temp sensitivity got me thinking..

You all go by *weight* when you create a powder throw correct? However, what you really do when you set your throw on your powder measure is you set a *volume* which just happens to correspond to a specific weight, on that specific day when you set up the throw.

And I'll bet you all keep powder in your powder dispensers when you aren't loading correct?

Well, here's a little secret... All powders are *hygroscopic*, they absorb moisture, some faster than others, this has 2 effects. 1) it causes the weight to vary over time; it causes the size of the pellets or flakes to vary in density. Both of which effect the actual amount of powder you put in a case.

I don't know how to fix the above however, and yes I do the same.

One option, but it's a RPITA, is to always empty your powder measure after reloading sessions, put all the powder back into a sealed container and on each reloading session, re-adjust your measure to weight. However this still doesn't fix the *what* weight is the right weight given how much or little the powder has changed.

I know all of this happens at a very small rate, and it will also vary with lots of powder, but it is something that you need to think about when you start to chase a velocity change, or all of a sudden weight change, etc.

On a side note, I also suspect that loading on very humid days will effect velocity of bullets from those rounds when shot, but I don't have enough information to prove that theory....

Alan

[SN13]

I made the mistake of leaving my RL22 Powder in the garage in my hopper when I was reloading .270win. The first session had really good accuracy in the gun. As the weeks went by the reloads got more and more erratic. I don't leave powder in the garage anymore. It's all inside in the AC. FL humidity in the garage killed that pound of powder. Just my anecdotal evidence.

[jcc7x7]

Great idea BUt I wonder how many of us will do it.LOL

[Sin-ster]

I do half of it, at any rate. The powder always comes out of my hopper at the end of a session. It's a PITA at times, but you get pretty good at it after a while.

Being a natural pessimist, I don't really trust the scale as much as I do the chrony and the look of the primers. So I work up a load and reference the weight, but make my decisions based on the velocities. Once it's fixed, I write down what my scales say, but most importantly, I don't touch the hopper adjustment. Combined with the previously mentioned practice, I've had excellent results in terms of consistency.

I do load in a humid climate, though. So good food for thought!

[bajadudes]

I have been taking the powder measure off the 1050 and putting it in the gun safe where the golden rod heater keeps it nice and temp controlled. I also make it a habit of always keeping the powder jugs capped and sealed unless I am pouring out of them. Being from a fireworks making background I have found that the humidity and hygroscopic properties of powders have a big effect. For instance we never made red stars on humid or cloudy days. They would loose color and be pinkish instead. The strontium nitrate used in that formula was very hygroscopic.

The nitrocellulose used in modern smokeless powders is not very hygroscopic but the stabilizers ( mostly calcium carbonate which is a salt )and other additives like potassium chlorate and nitrate as flash suppressors are. Best bet as the old saying goes is to keep your powder dry. In fireworks making and the production of other explosive powders we tried to keep an environment of about 35 to 40% humidity. much drier and static charges become an issue, much wetter and hygroscopic problems begin to arise.

[Saffer]

Some food for thought, and may be the reason my Dillon 650 throws such erratic powder measures. That and the massive temperature/humidity swings we experience (Canada). Perhaps I should be more disciplined at emptying the hopper, and see if that makes a difference.