I bought this rifle used from someone off of here and ever since I received it I noticed that the bolt is heavy or sticking whether dry firing or firing a round. I didn't think much of it but it has gotten worse. I was told rifle had approx 80 rounds down it. I have put about 100 more. I pulled the bolt apart, wiped it down, oiled it and it's still heavy/ sticking when dry firing. It will run smooth if the trigger is not pulled. I didn't see anything obvious upon teardown. There is a wear mark in the channel of wear the cam contacts. Firing pin is not bent. I put a dab of grease there but no difference. Any ideas?