The shroud visuallyis the part of the bolt behind the handle.They are designed to shield the shooter from gases that may occur as a result of a cartridge malfunction. All Modern Guns and military rifles of a 100 +year old design have some way of shielding the shooter from these gasses. Some are more effective then others. Theoretically closed end shrouds block gassess more efficiently. In actual practice having had 1case failure with aRemington which has an open end shroud I never noticed one puff of gas even though the gas burned a nice neat 1/16" hole in the bolt face.