What OAL are you using? Different bullets have slightly different bullet nose shape (ogive) that may allow the bullet nose to hit the start of rifling.
Using Unclenick's guide, take the barrel out of the pistol and do a barrel drop test to determine the OAL (your round should drop in freely with a "plonk" as the case mouth headspaces on the chamber without bullet nose hitting the start of rifling). Once you determined the OAL that works with your barrel, then conduct a full powder work up with the new bullet load to determine what powder charges reliably cycle the slide.
