Thank you for your reply . Yes it is a Wiselite MkII . It came with 2 barrels . they will not change out was they should . They need way too much persuasion if you know what I mean .I striped the receiver and cleaned it and could not find any thing in the barrel nut area that looked like it was causing the hard fit . I made up a polishing rod covered with 0000 steel wool and cleaned the area in front of the breach bolt . The barrel nut works very easy and seems to fit in the receiver with no slop .