Drew, I have to ask some questions, as once upon a time, I had the exact problem. The cause was shocking to say the least.
1) Prior to attaching the scope, was the rifle functioning properly?
2) What kind of scope mount did you use?
3) Remove the op rod spring and do a tilt test, starting when the bolt is in closed position. What happens? Is there any binding? Does it bind anywhere near the scope mounting screw? Check to ensure that the screw is not protruding into the groove (where the bolt slides).
Here is what happened to me. I installed a scope mount from NC Star. I even posted some pics. Anyway, to make a long story short, I did not do a tilt test. What I did do was re-assemble everything and out to the range I went. Just like you....had a single action. I chalked it up to cheap grease and cold weather. Took it home and inspected. Yup, you guessed it...the screw...and a hard little bugger at that, was protruding into the groove long enough to cause the bolt to bind and lose too much energy. I ground the screw down and .... she was back to normal.