A FLASH SUPRESSOR is what reduces that visible flash you are talking about. Also they seem to be more effective than you imply but still less effective than a sound suppressor which eliminates muzzle flash and reduces muzzle report significantly, while also reducing recoil. I also believe one of the reasons for having flash suppressors on military weapons is to protect the crown from damage, which it does quite well.
I recall my armor(decades ago) saying the only good thing about the flash suppressors on our A1's was that they protected the crown.
The device on the .50 cal Barret both suppresses the flash and reduces recoil; Doesn't it?