[22WRF]

The Model 60 has a manual bolt hold-open, activated by pushing the charging handle inward towards the gun when it is in the fully-retracted, open breech position. To close the bolt with the manual bolt hold-open engaged, the charging handle must be pulled out, away from to the gun, before the bolt will go forward. Since 1985, the Model 60 has also included a patented automatic "last-shot" bolt hold-open. This latter feature is a safety feature that locks the bolt half-way open after the last 22 LR cartridge is fired, thereby allowing the safe inspection of the now-open action.
Yours was mfg in 1976