Charge Weight Changes With Temperature, Humidity

[Donny1]

I had not loaded anything in a couple of months and everything was still set up for my 9mm range loads. I sat down today to load some rounds and the first thing I did was check the powder drop. My powder measure and balance scale were set to 5gn of CFE Pistol. The bottle of powder is the only one on the bench and the powder measure was still half full, with the cap on top from the last session.

I cycled it 5-6 times and then checked in on my Ohaus balance scale. It was throwing 4.6gn every time. Checked it on an electronic scale as well, 4.6gn. I made the adjustment and I've loaded a couple hundred rounds and the measure is still right on.

Last time I was loading it was slightly cooler and likely the humidity was a bit higher but I've never seen any noticeable difference before. In reality where I live things don't change a lot. Humidity today is 8% and it's 85 deg. Last time I was loading it was high 70's and 10-20% humidity, not much of a change.

The only thing I can think of is that the powder measure is not air tight and the powder got dryer than what was is in the sealed bottle. Is this a thing? I plan to load a bunch of these over the next week and I check the charge every 10-20 rounds so I'm curious if it will change when the fresh powder gets metered.

Always checking myself, always learning.

[hermosabeach]

a few thoughts


When done reloading- return all powder back to original container....


I know we think we can tell bullseye green green dot.... or 700X


just return the powder back to the container....



2-
I would pull the bullet from one of your last reloads and weigh the powder...

Simply verify the powder charge in the round

[PoorRichRichard]

I notice variation with temp and humidity changes, but I'm reloading shotgun primarily in 20 and 12, so I don't care much about a grains' variation in my loads.

[JackEllis]

Here's something to read on the subject: http://bulletin.accurateshooter.com/...er-burn-rates/

I assume your powder dispenser measures volume so you apparently observed an 8% decrease in density *if* your powder drop metered out the same volume before and after. The article above suggests powders sent from the factory have a moisture content of 1%, presumably by weight.

I'm also thinking you might want to go back to the "before" rounds, take one or two apart, and weight the powder. Before might not be what you think it is.

[Donny1]

All those rounds already made it down the barrel(s), that's why I'm loading again. All I have is boxed ammo in all calibers except for .223 and I don't want to go in to those supplies. Going to be hot here for the next few days so I will stay inside and do some loading.

I think this is the first time I didn't return the unused powder to the container and that is likely the difference. As far as telling powders apart, I only have the powder I'm using on the bench, the rest is kept in a cabinet, same with primers.

Thank you, good read. If in fact dryer powder burns faster I will be able to tell as I have run these on the chrono, several times with the Shield all the way up to the PC9 with a 17" barrel. Also it won't hurt as I've found the CFE pistol runs slower fps than the data, but that could be because my projectiles are not the same exact ones, same weight/profile though as in published data. But is seems that way across the board. Not a big deal because these are far below max loads, just practice ammo.

Just FYI:

Xtreme 9mm 124gn CPRN
5.0gn CFE Pistol
COL 1.125

Shield 1034 fps
PC9 1266 fps

If you haven't used CFE Pistol it runs a bit sooty on the low end but is very reliable (ES).

[pennstater]

Here's something to read on the subject: http://bulletin.accurateshooter.com/...er-burn-rates/

I assume your powder dispenser measures volume so you apparently observed an 8% decrease in density *if* your powder drop metered out the same volume before and after. The article above suggests powders sent from the factory have a moisture content of 1%, presumably by weight.

I'm also thinking you might want to go back to the "before" rounds, take one or two apart, and weight the powder. Before might not be what you think it is.

I'd do a couple of the "before" rounds just to verify. Can't hurt.

MLC

[sofbak]

After sitting for a couple of months in the hopper, the powder experienced a mechanical density increase from settling due to gravity and/or vibration.

Vibe settling could come from several sources: open/close of doors near the press/powder hopper, other activities on the reloading bench and so on.

Dollars to donuts bet: empty hopper, refill hopper, and with same throw settling and same scale settling the charges will return to previous measured weights.

['ol shooter]

I use a micrometer adjustment on my Uniflow, and it needs slight re-adjusting every time I use it. I use Titegroup and CFE Pistol, they both flow real nice but still need that slight tweak to get it spot on. I do not leave powder in the hopper.

[LynnJr]

Powder left out tends to lose weight not gain weight like many believe. It doesn't absorb water from humidity it outgases.
The results can be found doing a Google search of Benchrest Central and Henry Child's.

[JagerDog]