Watch as U.S. Marines with Company B, 1st Reconnaissance Battalion, 1st Marine Division, engage enemy forces from a patrol base near Sangin, Afghanistan. The footage, from 2010, shows Marine scout snipers as they perform counterinsurgency operations.
I would not bother doing that when ambushed. Wouldn't even have time to think about it. The thing was zero'ed with the can anyway. Instead, matter at hand is to destroy by fire and manuver and lay as much aimed fire down as needed, rather than finger that barrel attachment. It is providing a reduced muzzle blast and of concussive effect which is desirable. Still loud but for the operator and especially those on your flanks it makes life better. I'd leave it on just not to tick off my fellow Marines. I'm not even sure what the shift in POI is. I had the older M82A1 and did't have a can. For about 5 yrs I wish I had one. It's not much extra to hump.