Help needed to determine whether an 81mm mortar shell is a live one or a dummy one

1967 FA 81mm mortar shell recovered from PA proving ground was supposed to be a ‘dummy’ but it seems to be more than just a sand-filled dummy (as I was told it was.) In prepping it for sale, I checked the markings and the primer. It’s marked HE and has been fired. The nose plug is non-ferrous and has spanner grooves. I was able to loosen the plug, and removed it by carefully working it back and forth with the shell upright. (Since it had no markings to identify it as inert I decided to be overcautious.) The booster cup is filled with some kind of granular material that looks like crushed metal slag, it has a crystal-like appearance up close. I loosened the booster cup by slamming the shell on its head a few times and then used a wooden blade to pry it away from the shell. As you can see, there is some kind of soft, white filler in the explosive compartment of the shell. I’ve stopped there until someone can help me identify this round as either explosive or inert.