[E.Allen]

Flash suppressors on .223 will decrease, but not usually eliminate the signature. Sometimes they even enhance the flash by sending a bright jet out all vents in a large star shaped display.

I've only seen them practically eliminate the flash when using military surplus ammo (military uses flash suppressants in their powder).

Commercial ammo usually flashes much more. I would presume he's using commercial ammo because the bullets are repeatedly reported as fragmenting in the victims. This would indicate hollow point or soft point ammo, those are commercial types, military would be FMJ (full metal jacket)

These are observations from being on a night firing line with about 20 .223 shooters, the short barreled 11.5 inch
AR type gave a pretty good flash even with military ammo and a flash suppressor.

.223 out of a short barrelled pistol (flash suppressor unlikely on a pistol barrel, they're made to fit threaded rifle muzzles) would have a HUGE muzzle flash.

[FootBall]

Commercial ammo usually flashes much more.

If I heard correctly a few days ago on TV one time. The sniper is making his own .223 bullets. He could be incorporating the anti-flash powder in bullet when he makes it.

Disclaimer: I'm not sure if I heard this correctly or not.