decided to load three boxes of brass for my 30-06 since I had the time tonite.I was loading 47 gr of imr 4320 with a 150 gr hornandy.Pretty mild load,actually.Got everything set up and started loading.Had two different cans of powder,one unopened,one less than half .I decided to mix the two together.I poured the smaller one in on top of the unopened one and gently mixed..About half way through the brass ,the powder started getting lower in the powder measure,and I refilled the measure tube.I checked the scale,and it wouldnt balance.
The charges had gained three grains up to 50 grains!
Only thing I can think of is the unopened can of powder is much denser than the open one!Nothing else changed and the scale still balances when empty.Now I feel I must pull all the rounds and start over.Good thing its only july!!

Yes, powder will vary slightly in density, but not that much. There are too many variables in the situation you describe to make a dependable guess as to what went wrong, but suffice it to say that the slightly different densities of the two lots of powder did not make nearly an 8% difference in charge weights.

Some people believe that the moisture content of powder makes a big difference. Not so. Most powders are very close to the specific gravity of water, therefore it is largely irrelavent to its density how much moisture powder has absorbed. On the other hand, powder with a high moisture content has just that much less actual chemical in it, so 50 grains of low-moisture powder contains more BTUs than 50 grains of high moisture powder.

With VihtaVuori powders it change very little. I don´t care it at all.

I agree with Stonecreek, 3 grains difference between lots of IMR powder is unheard of. Your scale and powder measure settings may not have changed, but something did. I would suspect that extruded, stick type powders like 4320 tend to bridge somewhere in the measure, making some loads light and others heavy.

Personally, I only use direct from measure to case using spherical\ball powders. Extruded go from measure to scale to case as almost every throw on my Uniflow cuts some grains.

Stonecreek's assessment is right on the money. A three-grain variance is simply not attributable to a difference in the powder alone. Something else is amiss.

well,I pulled 20 of 35 rounds loaded,and so far ALL of them have 50 gr of powder.
I still have no idea what went wrong.
Looks like all of them will be 50 gr.Probably not an overload,50gr is the max load in my hornandy book,but I am using military brass.no sense taking a chance,46 gr worked great last year,but pretty mild.
But Im not going up 4 grains.
Pull'em all, stupid.