Wow. I do crimp my 300 loads and do use magnum primers with 1680(subs). I've not had any problems unburnt powder. I shoot this andjust about all other 300 blk reloads suppressed.Likely true.
I shot some A-1680 in my 454 Casull which were hot loads and they were squibs, stuck bullet in the barrel. The powder sort of fizzled and the granules were all over the place but were a sandy color. Looked like I dumped sand in the action. I contacted Western powder about this and they never did figure it out. They suspected that the load was a bit light but it was compressed, then thought a heavier crimp might help but I just stopped using that powder. Perhaps you arent getting a complete burn. Magnum primers may work better for magnum ball powders.
I could always use more 1680 if you're looking to "unload" it.