I’ve read some horror stories that involved gunpowder residue.
I’d just buy a brand new bag.
The gunpower residue thing has happened to me. I got severely groped, and after some delay was sent on my way. I was groped enough to think I deserved a steak dinner, or a least a few drinks. But no.
Residue can bring on a scrub by a sponge-like instrument on the suspect bag. Had it happen to me once. After the scrub, I asked the officer what had set off the scanner, and he said "gunpowder." I had used my ammo bag for an extra carry-on! After verifying the bag's contents, I was on my way!