IMR3031 ancient vs new

[Don1357]

This was mildly interesting. I was using some old IMR3031 from an old square metal can do do plinking loads for my 45-70 rifles. The RCBS Quckcharge was doing a reasonably good job at keeping the charges at 50 grains but when I ran out of the old stuff and switched to a fresh plastic tube same volume was dropping 54.5 grain charges... I didn't expect to see almost a +10% difference from one to the next. The cartridge volume was equally affected, went from 100% capacity (Hornady short brass) to pretty much 90% capacity.

[Winger Ed.]

Sort of a similar thing happened to me. I went from new to old with 4198. The old stuff was in a sealed can with a $2. retail price sticker.

I'd had a bunch of it, and found a load for 7.62 in a old Cartridges of the World book, and used it.
The same weight of the old 4198 more filled the case, but I didn't think anything of it until I blew up a Springfield M1A.

My guess is that the solvents used to make the old 4198 had dried out over time.
Each little speck had the same energy as the new stuff does, however; being dried out, they are lighter.

The same weight of old stuff gives more volume and more individual specks than the new.
Hence, I had a overcharge without realizing it.

After that, I still use old powders, but put it on 'double secret probation'
with a few of the most minimum loads until it proves that it will behave itself.