Certainly they will require "fitting". How many barrels have you tried from one double, to the next, that fit. Some may be close but it is rare for them to fit. I have fit a few barrels from one donor gun to another and found it takes a few minutes to more than I can do without a few choice words. Luck of the draw for 2K. I would have them fit them. If they can not do it tell them to keep the barrels.