If the trigger has not been "tweaked" by someone without knowledge of what to do then it is probably gummed up or has a piece of dirt lodged in the sear engagement surfaces. To clean, remove the stock and pour liberal amounts of lighter fluid into the trigger with a bit of air blown through (you can use canned air for computers for this) and as mentioned do not oil or use WD-40 WHICH IS EVEN WORSE. To test the trigger work the bolt smartly and the striker should not fall, then #### the bolt and put on the safety and pull the trigger then release the safety and rap the butt of the rifle smartly on a carpeted area, again the striker should not fall. If any of these tests fail or you are not confident take it to a gunsmith. By the way the only rifle I had that fired without pulling the trigger was a Browning A bolt that got some grit in the trigger that made it unsafe until cleaned.