Definitely not factory 12/20 set, as they never offered the XT in a 20ga. Like Bob K stated, the 20ga was probably fitted later. All XT's are Invector Plus chokes. One thing that stands out to me though with what you said, you stated the receiver is blued? As far as I know, all of the XT's had the nitride (silver) colored receiver. This could be an older model Citori Trap with a blued receiver, in which case, throw everything I said out the window. The gun could be Standard Invector or Invector Plus, could also be either short or long tang on the trigger guard. If you can get the serial number off the receiver, you can go to Browning's website and see exactly which model it is. Garrett