Temperature Sensitive Powders

[BigTinVA]

I have seen several posts where a person describes a particular powder as being temperature sensitive in that the cartridge produces lower velocities when shot in colder weather. My question is, can the temperature affect the weight of the powder charge at the time the cartridge is being loaded? It seems that I get a slight variation (usually +/- .1 sometimes .2) of charge weight on my scale from one day to the next without ever adjusting my powder measure between loading sessions. It may just be my powder measure, but I was curious about the affect different temps while weighing charges. I try to be very consistent in my operation of the press, a Dillon 550. Thanks for any input.

[HSMITH]

No, temps don't change the weight of the powder. Humidity can, but it is very very slight unless the powder is stored in an open container for a period of time.

[nhglyn]

I believe the posts you have seen refer to the difference in fps, therefore pf, of bullets being shot in different temperatures. Example: A bullet with powder X will chrono at 1380 fps at 40 degrees yet the same bullet might chrono at 1330 at 75 degrees. I had this problem with IMR 4756 and have switched to VV N105 which, for me, does not show these temperature sensitive changes.

[shred]

Temperature will change the volume of the charge bar in the powder measure, especially the all-metal Dillon ones. It won't be a lot however.

But, that said, I've been researching reloading scale tolerances. Most of the digital ones are +/- 0.1 grain or more, so a 0.1 grain fluctuation could just be the scale one time to the next.

[L9X25]

Another factor that can change charge weight, from day to day, is settling caused by vibration. If I continue to load after the "out of primer" warning buzzer starts, my load is usually ~.2 grs heavier. Since my load is about 16 grs, and not near max load, that is not dangerous. It is significant enough that I will not continue to load without stopping the buzzer.

[mlmiller1]

For you really smart guys, has anyone considered whether different barometric pressures will give different charge weights for the same setting on your powder drop? I've noticed from day to day, without changing anything on the loader, approx same time of day, same temp, roughly the same humidity, that the powder weight seems to vary approx .1gr up or down & the only difference I can point to is a variation in the barometric pressure. Is that possible? Like Shred says, it may just be the scale, but as far as outside factors, pressure is the only difference I can find. Just a thought, anyway. MLM

[Justsomeguy]

A powder measure that goes by volume rather than weight will have variations of .1 or sometimes a little more. These are not significant differences as other factors can and will change the actual velocity of the round more than the small difference in powder charge. These include, but are not limited to:

Minute differences in the hardness of the bullet

Minute differences in the bullet weight

" " in the bullet size

fouling in the barrel as you shoot

differences in the brass size and hardness... how it grips the bullet

the heat of the chamber as you shoot

small differences in the primer's ability to light off the charge caused by a series of factors

small differences in the brass capacity

small differences in bullet seating depth because of bullet length etc.

the individual powder's resistance to lighting off

the temperature of the air when shooting

All these things and more will affect shot to shot differences in velocity at least as much as the small variation in charge weight. If .1 is the most variation you are getting you are in good shape.