Not to get too off topic but; Does anyone use volumetric 'scoops' such as the lee powder measures?  If so, how consistent are they compared to those super fancy scales or powder throwers?  I am able to reload perfectly adequate handgun loads with those but I have never used it to try and make accurate rifle loads.

Most shooters don’t take the time to learn how to use their powder measure accurately. They take it out of the box fill it full of powder and off they go. What powder you are using and how you handle your measure has a lot to do with how accurate the drop will be. First what powder are you using, stick powders will meter differently than ball powders. This is why so many have trouble metering 4759 its shape doesn’t let it settle uniformly in small drops. The larger the drop the more room in the chamber the powder has to settle. Some measures were just never designed with tight enough tolerances to handle ball powders. Ever worked your handle and felt that crunchy feel? Time to buy a new measure that was designed for ball. 
When you get a new measure spend some time with it to find out how it wants to be used. You will find that after you refine your technique you should be able to keep your SD’s around 10 F.P.S.

40 Rod

CF after re-reading my post it did not quite come out in the positive manner it was intended to so I simply removed it and I apologize if it was taken wrongly.

JLouis

John I have noticed that my weights will vary slightly during the year when being dropped from my Harrel Schuetzen measure, same lot of powder and same volume setting. Could this be attributed to moisture gained or lost as I really cannot say for sure and would only assume so. I have also noticed that if I chase the weight my results on the target seem to change more than if I just maintain the same amount of volume. You picked a very interesting subject in regards to maintaining the same velocity from one outing to the next and thus the same degree of accuracy. It is also not untypical to have to make a small change to the powder charge for every ten degrees in temperature change for a load to stay in tune and to continue to provide the least amount of vertical dispersion. Would you think it is the burn rate that is changing or possibly the weight of the charge due to moisture being either gained or lost of which would also affect the volumne. It is all somewhat of a mystery to me but I do know the jacketed benchrest shooters thpicaly make small adjustments after every relay and the reason for thier reloading at the matches. I would tend to think that if one loads by either weight or volume if match shooting either or would just be simply be a good place to start out the day and then adjusted as required. If shooting pre-charged cases or fixed the best approach might be to use the average over the long run either by exact weight or volume and to run with it and hope for the best. When I was shooting my 32Miller Short with pre-charged cases I never seemed to get the load quite right for the day and so I got rid of it and went back to the 32-40 of which is quite abit more forgiving and using one case so I could adjust the powder as the changes in the verticle dispersion were occuring.

I hope this isn't taking it off topic but I think it is all relevant to your original question as I understood it?
JLouis

Quote:

John, my presumption is that this is true.   
I have never weighed a given sample of smokeless fresh from an unopened container - left the cap off and then periodically took additional weighings to determine weight loss or gain. Plus the average moisture in newly produced smokeless is a subject I've never read about

Blackpowder - different story.  The drying process of Swiss powder at the plant reduces the moisture in the powder to 0.5% - then packaged.  Add BP is hygroscopic.  Open the container and how much additional moisture is absorbed = ?  But it happens.  This will impact the density of the powder grains and change the volumetric measure of BP weight when scale weighed

Some plastics do allow moisture to move through the wall of the container. 
Some who have used brush-on polishing compounds have removed the cap from a properly sealed container to discover that the polishing media has dried out while sitting on the shelf.

John
I have noticed that my charge has to be adjusted slightly for best results. This is a subtle thing sometimes I will shoot 5 or 6 groups before deciding to add a click of powder. Then I shoot 2 or 3 more to see if it helps, sometimes it’s just me. Of coarse powder has to be adjusted for different lots of the same powder every once in a while they will shoot the same but usually I will have to add or subtract a click to my base load to get best results. For example the newest lot of Enforcer required a 1-click addition to get the same group size average than I got with the old 4100.

40 Rod

No argument with your methodology John. The results are there for the world to see. Beyond World Class. Nice to say the least.