30-06 Powder and Cast Conundrum

[TCLouis]

Years ago a friends wife went from her trusty lever gun to an A bolt.
She was concerned about the difference in operation and the cost/recoil in getting used to the new gun so I offered to run up some cast loads for the purpose.
Push come to shove I got part of a box of loaded rounds back.
I needed entertainment the other day while letting a gun I was testing loads for cool down between groups so I drug out the trusty 03 BOOLIT gun. Entertainment, empty the brass, and get some extra shooting time in worked for me. Well the load I put up all those years ago shot very well so when I got home I broke on down, unknown primer (likely WLR), 150 RCBS FPGC, 16 grains of powder.
WHAT HE HECK POWDER IS THAT??????
I do not recognize it as any powder I have, not a spherical, flake or rod shape. Small particles in physical size.
Why didn't I label that box of rounds, I would like to duplicate the load because it shot very well.
I have poured powder out of every container I have and none are even close. I have run out of only one powder but can not imagine using it and certainly not at 16 grains.
Gist of the story . . . .
Label, Label, Label the load information.

[MUSTANG]

Years ago I never labeled any of my reloads. Being a poor Marine; I would shoot it up as fast as I could afford to buy components and reload it. As times and the wallet improved; I ran into the same problem as I would have a box of .45ACP, or 30-06's, or 7.62 that I did not know what boolit/Bullet was used or the powder - but shot them up any way. It dawned on me that I needed to change my ways and I still open some ammo cans from way in the back (physical and time wise), but find at a minimum hand written notes if not labels. We live and hopefully learn with experience.

[ShooterAZ]

If it was one of my cast 30-06 loads with 16 grains of powder, the powder would likely have been 2400. But yeah, labeling your loads will take guesswork out of the equation.

[Gewehr-Guy]

If you used to load for a .357 magnum or .22 Hornet, the unidentified powder could be 2400. Another possibility could be SR4756, but that powder is not made anymore. For a good load, just try to find some more 2400, and start there.

[15meter]

16 grains of 2400 was(and is) my 06 go-to plinking load. Does it look like 2400?