Yes, the Bulleted Blank 'Masher' types I worked on. Has a vertical hole drilled to one side. & a pin fitted to prevent it unscrewing during firing. I can only recall that much later Barrels & you will remember this too. 7.62mm LMG barrels that were selected for blank firing. Had an E.M.E.R Instruction, to drill right through the barrel transversely. Fit a nut & bolt & stake the bolt shank ends. To prevent the nut unscrewing. & then paint the front 8" or so, Bright yellow, Paint' Heat' Resisting. Or as you say Paint, bright Yellow, High visability, Armourers Bicycle, Theft preventing, High Profile Colour!...:lol:
For those that are not familiar with this Modification. The bolt acted as a 'Choke' to restrict the flow of gas down the barrel. To a point where it slowed it, enough for some of the Gas to be tapped off. To drive/ cycle the action.
Later on in service. A detachable Blank Firing Attachment was introduced. So that the guns 'Normal' Barrel. Could be used on exercises for blank firing. The amount of blanks used on exercises, was deemed insufficient. To wear the barrel to any detrimental degree. :wave: