Pull the charging handle back, and the front face of the bolt should stop about 1/8" to 1/4" in front of the back edge of the ejection port window.  if the face of the bolt is farther back, or not far enough back for this dimension, then you have a problem with the receiver extension, the buffer spring, the buffer, of if a fixed stock butt stock screw being too long and protruding into the back inside of the receiver extension.  

As for recoil spring lengths, 10.5" for a carbine spring, and 11.75" for a fixed stock.  Also, when you are checking the spring length, make sure to knock off any end of coil wind burs from the spring, and even flush the buffer bumper roll pin to the sides of the buffer.


Pull the bolt off the carrier and using just the carrier with key, dry fit the carrier into the upper receiver make sure that the sides of the key are not binding on the upper receiver slot/U slot of the charging handle, and the gas tube is is correctly indexed with the carrier key.


Short of these problems, go back and make sure clean the rifle correctly to remove all the old storage grease, including scrubbing the chamber with a CLP and a chamber brush, then make sure that you are correctly lubing the upper receiver bearing areas, including the buffer, spring and inside of the tube. From there, need to start checking for binding/gas blockages/gas leaks, such in the case of the gas tube/barrel leaking at the gas block, or even the carrier key leaking at the top of the carrier.