There is actually a video of a man with a helmet cam getting suppressed in a gun fight. He took cover in attempt to avoid incoming fire, it kinda helped. the underbarrel grenade launcher was hit. guy was fine.
For the breach gun using a surrounding canister for it to slide and twist into would provide a bit more coverage.
During the landing at D-Day a soldier was literally saved by the internal magazine of his M1 Garand rifle when a round from a German MG-42 struck the weapon which had been held in front of his chest, knocking him to the sand. He went on later to live through the war and share his story.