Some time back, my son and I were shooting (plinking) in an old quarry. The place was very dusty & windy. We & our rifles were soon covered with dust. My son was shooting an Argentine-made Mauser Model 1909 with a very pronounced flange on the bolt sleeve. He had a case head separation, with a lot of gas coming back through the action. I was on his left, watching him shoot and saw dust blown back against the bolt sleeve flange. Gas may or may not have left via the thumb cut, but the flange is what kept the gas out of his face.
