I've never had significant leading in my S&W model 28 with full power loads and 158 grain cast SWCs, and I've used some pretty stiff charges of 296. Other loads have used 14.5 to 15 grains of 2400 with good results as well. Note that 15 grains of 2400 is almost certainly above max in most manuals for cast 158 grain SWCs now, but it used to be a pretty standard magnum load.
I've been casting my own for a little over 5 years now using RCBS 38-150-SWC, but prior to that I bought Lasercast 158 grain SWCs. The Lasercast are extremely hard--much harder than my own cast bullets, but neither leaded my model 28 at any velocity.