On another forum I am watchig a thread where some wildcat shooters are pushing the envelope with max loads and one was talking about how he left a pan load of powder on his charge master and in a few days it had lost about 1% of its weight. (about a half a grain on a 50 grain load).

My initial comment was that out to 300 yards you probably could not shoot the difference in most guns.

The reply was they were shooting gongs at 1000 yards and a few fps meant the difference between a hit or a miss and at the top of the load data ta half a grain was overpressure.

So my question is - has anyone ever tested fresh powder versus "old" powder to see if it has a significant effect.

I can design a good test for this but am too lazy to set it up and would rather hear you guys thoughts on it.

I would think weighing powder down to a gnat's eyelash may be satisfying, but it is essentially meaningless for us hunters. It's like measuring firewood to the nearest thousandth of an inch. Bench shooters are a whole different class.

A few years ago I did test this with opened and sealed Imr 4064 powder and over a period of 30 days (1 month) the can that was unsealed weighted less according to my digital scale than the sealed can. Now it was right around 1%- 1 1/2% that the unsealed powder weighted less than the sealed powder and the only thing I can attribute to the loss of weight was the solvents used in the powder that evaporate over a period of time especially when the cover is left off for a month.

The last time I tried it, due to the humidity in Sydney, I actually GAINED few tenth of grains in the tray.

I don't know what volitiles would be used in the manufacture of smokeless powder unless it was alcohol but I haven't made any for - oh - about - 62 years.
I do keep my powder cool and closed so I don't know whether any loss would affect the performance or not. That might be a worthwhile experiment some day - I'll put it on my list.
I will weigh out ten identical charges - five will be placed into cartridges with bullets on top and the others will be placed in cartridges with out bullets. (I will cover them to keep dust and bugs out but it will be covered with cheese cloth. I will wait a month and then finish loading the bullets and fire them over the chronograph. I know for a real double blind test I should have a mess more loaded and only numbers on them and then record the numbers on a separate sheet with the loading and then shoot them recording the velocity and the number on the bullet and finally compare the velocities with the load history but it seems like a lot more trouble than I want to go through.
I do usually fire at least twenty rounds to get average velocities and standard deviation... Still seems like a lot of work though because I don't think it will do anything to the performance - unless they are stored in direct sunlight or with a UV light shining on them.

As Gelan said, the humidity out here in Australia can cause some problems, but like the majority of us...I have never actually conducted any tests. My powder is in one of three conditions:
1. Sealed in it's factory container,
2. Sitting in the case for a matter of minutes, waiting for a projectile to be seated, or
3. Sitting in a loaded bullet awaiting a fast trip down the barrel tube.

I would have thought that any volatiles used in the manufacture of the powder would be well stabilised in the product by the time it leaves the factory, however a quick test with the sniffer tool, the Mark 1 Nose, shows that there is something "leaving" the powder because you can smell it when you open the container. Exactly what this is, is anybody's guess, and I would imagine a million dollar complex piece of machinery would be required to show exactly what is leaving the powder.

My thoughts are that unless the powder is left out in the open for a considerable time, any change to its power would be negligible, although Paul brings up a pertinent point with the mention of direct sun and UV.

Hmmm, I've already run to many tests. I would think that temperature change would have a more significant affect. I lose 40 fps between shootingin the ssummer and hunting on a cold winter morning. That shows up in POI at 300 yards and beyond. In benchrest, everything counts and could be a factor at max pressure.

What about single based powders and double based powders? I would imagine there would be a difference between the two. I really don't think there would be much difference as a practical matter. Now if you loaded rounds from powder made in the 1940's then some from today, I would expect to see something. But remember, them benchrest shooters are a weird bunch. If they shoot bug hole groups wearing polka dot undies, and tie dye shirts, that's the way they will shoot from now on.

There are a bunch of powders by Hodgdon that are a lot less sensitive to temperature changes but most double base powders are dangerous below -30F. The nitro glycerine freezes and it detonates. I don't have to worry about that but I am considering switching to the "extreme" powders as they call them just because it is another advantage in keeping the groups small.

Bench rest guys are good folks. My rifle shooting rest was a gift from one of those guys. I was at the range and he was trying out his new rest and after about 20 minutes he asked if I wanted his old one. No money exchanged hands even after I volunteered - he liked the way I worked at making small groups I guess.

I don't know if this is one of you guys volitiles-but whenever I open a fresh can of 4895-I smell ether.Now I don't know if this is for preservation or an additive.And another thing- I have left that 4895 power in the powder drop for extended periods of time-up to 4 months by mistake and yes it does make the rounds when loaded erratic!It somehow devalues the powder,and is most noticeable in gas guns when shooting for group.Elvis -I have never heard about the -30degress f effect on powders-but i know at -20 degrees f mine still shoot fine!Chasin coyotes in the high desert of oregon in the winter I have encountered the sub zero weather several times!

Interesting you mention the ether smell Troubles. I have always been taught that if a powder smells "sweet" it is good, but if it smells "sour" then it is most likely "stale" and no good. This usually refers to powder that is old.

I have a tin of Nobel #2 Pistol Powder that is most likely 40 or more years old...and it is still sealed. Wonder what it is like now? Don't intend opening it just to see if it is still "sweet" though.

+1 do not use powder that smell "sour" it is off and will be quite dangerous due to unpredictable burning.

From the Alliant site.

How To Check Smokeless Powder For Deterioration

Although modern smokeless powders are basically free from deterioration under proper storage conditions, safe practices require a recognition of the signs of deterioration and its possible effects.Powder deterioration can be checked by opening the cap on the container and smelling the contents. Powder undergoing deterioration has an irritating acidic odor. (Don't confuse this with common solvent odors such as alcohol, ether and acetone.)Check to make certain that powder is not exposed to extreme heat as this may cause deterioration. Such exposure produces an acidity which accelerates further reaction and has been known, because of the heat generated by the reaction, to cause spontaneous combustion.

A little research reveals that even in a tightly closed container if exposed to 90+F for any prolonged period the powder will deteriorate. Single base powders go bad faster. I noted that ADI suggests a maximum storage life of 25 years.

As an aside but proper segway :-), where do you store your powder? I have mine in my workshop/reloading room in the basement. A friend at the range suggested I move it out to
the shed as it should get the same storage precaution as gasoline or any other flammable.

Storage, mines downstairs in the garage, in a sealed steel mortar box.
One would think that I would move it as I remember a news story from Ohio circa 1971 regarding a bloke that turned his home into a crater around 15 yards wide and really upset the neighborhood. He reportedly have over 100,000 rounds and a lot of powder stored down there.
My garden shed goes from -5 through to 50 deg c,with high humidity down stairs is a lot more temperature stable, might only get to 40 deg :-) .

Air tight steel containers used as storage for gun powder are bombs ready to go off. Make sure the container is vented so that if the powder does ignite it will only burn slowly and not cause an explosion. A vented and locked wooden crate with brass fittings is the best storage container for gun powder. Keep it cool and dry and out of reach of non-authorised people.

one of the places that I used to work for was throwing out some old metal filing cabinets,so I snagged a couple,they make a terrific powder repository!Loose fitting,temperature between 60-80deg f year round!And you can keep dif't powder types(rifle,pistol,shotgun)in dif't drawers!