I have had alot of lead fouling in my 2009 IL, MIM model 60 following a wadcutter diet.
The same ammo runs through my model 686-3 (1983), model 10-5,28-2 and19-3 without anything more than I might expect.

The model 60 on the other hand has significant amounts of lead in the first inch or so of the barrel. A brass brush and soaking over night with solvent doesn't begin to touch it whereas the older guns clean right up.

Has anyone else had this occur with ECM rifled guns and, if so, what has been your solution, other than switching to jacketed bullets?