I had two loads I worked up some serious overloads for carry in my P-3AT [ shirt pocket carry, 10 ounces when loaded] .380 pistol:

1) 6.1 gr Power Pistol, 90 gr Gold Dot, .967"

2) 6.5 gr 800X, 115 gr Win JHP, .975"



The 800X load was kicking allot harder, but when I used some 800X powder I left in the trickler for a month, the Power Pistol 90 loads kicked much harder.



What causes this?

Probably a couple of things. The flake powder may be picking up atmospheric moisture which reduces the amount of powder per weight thrown/weighed. It could also be the volatile factors (solvents) evaporating off, leaving powder with less energy available.

Furthermore, nitroglycerine's volatile. That's why nitro plant workers are subject to headaches, and why heart patients are supposed to throw out their nitroglycerine tablets and replace them after 6 months or so. Keep it sealed up.

Clark,

I dunno about the powders you specifically mentioned, but some experiments with Blue dot tell me that it does indeed change in weight per given volume as the humidity changes.

As in dropping 15 grains ( an arbitrary amount ) when the humidity is low will give a higher velocity/ pressure than the same 15 grains thrown after the powder has been sitting out for a while in 90+% humidity weather.

I imagine different powders will absorb humidity at different rates and capacities.
I keep all mine in the factory bottles when not actually using them.

Just .o2 and opinions from a less than labratory grade experiment.

Travis F.

Travis,

You are right about powders picking up moisture at different rates. Some are prone to picking up water/humidity and others aren't.

When I have left powder in the measure longer than anticipated (sometimes I just forget), I pour it back in the container and shake it up really well before using again. Dilutes out whatever changes may have occurred. You must be certain you know what you were loading last to do this, of course. Wouldn't want to get powder types mixed.