The "diamond" marks on your barrel are probably vise or wrench marks.  Possibly the barrel was clamped in a vise, when someone sawed the rifle barrel, re-crowned it, and mounted the replacement front-sight.  Such marks would be indicative of amateurish or careless workmanship.  They would not be found on proper arsenal work.  The #"7" stamped on your barrel probably identified a steel batch or identified a sub-inspector.