Same as out 120mm BAT guns. 120mm of back blast. I was walking back from one once after curing the M8C spotting rifle. No ear defenders. I tapped the gunner on the shoulder to tell him it was OK and walked out to the left for several yards and then to the rear as per the safety brief. Just then he fired off a couple of rounds from the M8C, I heard the word 'HIT....' and then the main gun opened up. The noise from the back blast blew my ears in.............