I have removed a few No 4 barrels with the shoulder cut method. You do not need a lath, in fact I used a small hobbyist metal saw blade and did it by hand. it takes a while to get the cut started and you have to do it carefully to make sure you maintain a small amount of metal on the barrel between it and the action, it is really pretty easy. The barrels were pretty soft any cut easily. Once the cut was deep enough a few hits with a hammer and the barrel(s) came off by hand.

You can also use a modeler knife to peel back the metal flange created between the front of the action body and cut, with the caveat you have to be sure the cut is deep enough. Works fine with a little Kriol to help.