oxygenated?

[XWrench3]

i just discovered that i left out in the open air, a medium quanity of IMR 4198 powder. it has been there on the shelf in both a dipping bowl, and the trickler for 2 days. is this going to be good yet, or has the air depleted some of the ingredients? i would think it would still burn, so if nothing else, i could make some plinking rounds out of it. but if i can still make good viable rounds with it, i would rather do that.

[Larry Gibson]

The "oxygen" required for the burn is part of the chemical makeup of the powder. It won't evaporate from the powder. It may have gained in moisture content though. The jury is still out on that as to how much ambient humidity has to do with burning rate. I'm not aware of a definative test, perhaps someone is?

Larry Gibson

[runfiverun]

i recall a test done once.
airc it stated that powder would suck up about 3% in water weight.
it would also lose weight in dry conditions.
might explain why i like 52 grs of powder in my loads [where i live] and someone else likes 51.5grs.
we could be very close in powder volumn. but off in weight just enough to make up the half grain from either side.
seems mostly negligable however as the powder will do it in a case also, unless sealed completely.
and you'd have to work up the loads with the sealer in place as it affects bullet pull.

[JIMinPHX]

Here in the Sonoran desert (Phoenix), I don't have much of a problem with that sort of thing. If you live in a humid area, then things may be different by you.

If I were you, I would load up about 5 shells from that lot of powder & try them out. If they fly just like all the others, then I would dump the powder back into the canister & use it as if it were new.

If it performs poorly, then I'd dispose of it.

[Mk42gunner]

I don't believe two days will cause any problems; but JIMinPHX has a good idea -- do a test.

I do know that solvents will evaporate out of powder, you could smell it when you walked into a ships powder magazine. This would depend on the composition of the powder,of course.

Robert

[HeavyMetal]

Powder is hydroscopic, although not as bad as brake fluid, and will absorb enough moisture to throw off your load if you set up a load before you left the powder out.

Fortunately the powder gets heavier with mositure not lighter which means you actually putting in less powder with the mositure content increased.

A lot of this is going to depend on what the weather and barameter are like when you left the powder out.

all in all I doubt you will be able to see a differnce in it unless it was 110 on the day you opened it and monsoon conditions the next day!

[XWrench3]

i thought i would update this, seeing as no one really knew. by letting the powder set out in the air for 2 days, there was a defininte loss in power and speed. just over 300 fps average between loads. i hand measured every charge, so it was not a volume issue. anyway, just know that if you are loading ammo for hunting, or trying to work up loads, if you let powder set out, use it for plinking, not good loads. at least this powder (IMR 4198). personally, i will just assume all powders are going to act this way, and err on the side of caution.