Interesting. I understand the ECM process has been used at least 10 years now. I have 3 S&W revolvers that fall into that time frame. My 686 (2013) and 627 (2016) have both run many hard cast lead bullets without excessive leading. As mentioned when I did have a leading problem it was with Xtreme SWC's and RNFP's and I was roll crimping through the cannelure band. SLT223 - You mention where you've not had this problem with any other Xtreme bullet. On their web site I'm not finding where they say it's made any different from the others. Did I miss that?
My new 69 has so far seen nothing but Xtreme 240gr. RNFP's and again, no signs of leading. Also, the rifling in all 3 are not rough at all. Comparing them to an older 629 the only difference I can notice is the edges of the lands might not be as sharp.