[Farnham]

So, I just bought another jug of Win748, and when I ran it through my Lee powder measure, which was metering out exactly 43.7gr with the last jug I had, it only threw 41.5gr on the same setting. I had to dial the measure back a little over two full turns to get up to 43.7gr with the new powder.

I had the last batch of powder for over a year (I moved right after I bought it, and didn't have my bench set up for a while), could it have absorbed water? Was the batch that much different? Anyone ever see this in "old" powder?

S/F

Farnham

[Kiwi98J]

It's good practice to "re-calibrate" a volumetric powder measure for each jug and lot and often as you work through the jug. Particle size, amount of broken particles, moisture (changes with relative humidity), exact recipe of the powder and condition of the powder maker extruder will affect density (weight per unit volume).

[P95Carry]

I think with variations in batches, there can be ''bulking'' issues. Thus a small variation in cutting of rods, or grinding of flakes etc - the volumetric aspect can alter marginally. After all - in large loads of 40 grains up say - one grain or so is a small percentage.

I agree - a batch is best tested re drop and then weigh. I doubt storage conditions will greatly affect this factor - batches being most likely source of small variation.

[Farnham]

Thanks for the replies, guys, I'm not an "old hand" at reloading yet, so after I reloaded 50 rds of .308 with the new powder, I started to get nervous.

Looks like I've got nothing to worry about, thanks again!

S/F

Farnham

[Rico567]

There seem to be three possibilities here. The first is uptake of moisture. Smokeless powder is not particularly hygroscopic (prone to absorb water), so I tend to discount a forty-odd grain charge gaining over two grains for that reason. Second, the measure was inadvertently changed- but you stated it hadn't been. That leaves a lot-to-lot variation in the powder bulk, which I suspect is the culprit here. Good idea to re-weigh your charge if you change lots. A ball powder like 748 is very high density, so it wouldn't take much variation in volume to produce the weight change you're seeing.

As for the age factor, I've shot reloads made with powder over 15 years old, and I noticed nothing different. I've never fired 748 that was that old, but I'm sure I've loaded some that was around five years.

[Redbeard55]

When I first got into reloading many years ago I got a series of reloading manuals from Dean Grinnel, Ed Matunas and one or two more authors. These were more how to manuals than actual load manuals. According to one of the authors, powder can definitely pick up moisture. Keep your powder dry applies to both black and smokeless powders. No careful reloader would ever consider leaving a powder container uncapped for long periods of time. In the book a powder sample was returned to a ballistics lab because of a noticed difference in charge weights. The ballistics lab was able to document that the heavier charge of powder was due to increased water content. There appears to be a step in the manufacturing process (possibly several) process where water is used. Depending upon how well the powder was dried during manufacture, this can account for differences in charge weights from lot to lot. This is one of the reasons you should always work up loads when changing to a new lot of powder. The difference in charge weight might be something as simple as moisture content, but the difference could also be due to a difference in burn rate, deterrents, etc. Since you don't know the reason, the only prudent option is to work up your loads again. A choronograph can be of assistance here

[redneck2]

I have an acquaintance that is a competition level benchrest shooter. He strongly believes that differences in weight are not as important as volume. For example, if he uses up a given lot of powder that weighed 50 grains and the same exact volume of a new batch of the powder weighs 49 grains, he'll stick with the original volume, not weight.

He says this explains why some load books tell you to use 50 grains and some will give 47 for the same components. May be identical amounts of powder by volume but not by weight due to density. He lives in Florida, so the powder may pick up weight if it picks up moisture.

If someone was real bored and wanted to try this theory with a few different firearms with new and old batches, it might be interesting