I see nothing on S&W's website or owner's manual to indicate that the TRR8 has polygonal rifling or a ported/compensated barrel, and those are the only two reason I can think of that unjacketed lead bullets would need to be avoided. In the manual, it does warn about ensuring that your chosen ammunition doesn't jump crimp under recoil with lightweight Scandium-frame revolvers and unjacketed bullets do jump crimp more easily than jacketed ones. I doubt, however, that would be so much of an issue with the TRR8 since it weighs substantially more than the all-steel Model 60 J-Frame and nearly as much as the all-steel Model 66 K-Frame both of which are also chambered for .357 Magnum.
