If the gun is a bolt action, pump action, revolver, or some other manually operated weapon, blank conversion isn't usually needed.
To convert a gun to fire blanks for a film, the barrel needs to be threaded for a Blank Firing Adapter (BFA). Some guns have external BFAs that screw on like Israeli blank adapters for AK-47s, but some guns need to have the inside of the barrel threaded and then plugged with an adapter. This blocks a certain amount of gasses so the weapon has enough pressure to fire blanks and cycle reliabley. Some guns need just this alone like the Walther P38 and the Beretta 92FS. But some guns like the M1911A1 need to the the top of the barrel milled around so the weapon will properly feed crimped blank cartridges.
And if the gun is adapted to fire blanks, it is ruined permanantly for using live rounds. If it was "modified" to fire blanks, it might just need a BFA added to the muzzle, but if it is "adapted" and permanantly changed, it is a blank gun only.
If I got anything wrong I'm sure the three armorers on this forum will correct me.
