I don't claim to heard of everything ever tried about gunpowders, but I'd not heard of such a thing as a flash retardant until it was mentioned here at TFL.
I have followed discussions about M-16 jamming since back in the actual days of Vietnam, and retardant was never mentioned as a contributory cause. Many other factors were mentioned, but I ain't gonna get into that again.
Chalk? Haven't a clue.
, Art