Mossberg Model 151M-B, .22 cal. semi-auto carbine.  NSN.  Very good condition.  20” barrel has excellent bore.  Barrel and receiver have 85% blue with some light surface rust.  Unique Mossberg sighting system with flip-up inserts for front and rear open sights.  Mossberg S130 swinging rear peep sight is missing sight disc.  Walnut stock has very good finish with few handling marks, tube fed magazine thru stock.  Factory sling swivels are missing.  Auto-loading action works fine.  A nice .22 plinker.  C&R OK.