For me it has long been first and foremost a matter of how well bullets fit chamber throat (in revolvers),having slightly larger chamber throat than forcing cone (again revolvers), bullet exiting cylinder throat being slightly larger than groove-to-groove diameter of barrel. This has been especially critical for hard cast bullets.
Stop blowby of hot powder gases past bullet and you will stop or greatly reduce leading. Good lube helps, as can proper sized gas checks (for velocities over 1400 fps).
SOP for lead bullets in revolvers is bullets just small enough diameter to allow easy chambering in whatever brass is being used, bullet diameter larger than cylinder throats, throats slightly larger than groove-to-groove of bore. Soft cast or swaged bullets have been essential for low chamber pressures (like standard pressure 38 Special) and often do not lead at velocities up to 1200 fps or more from revolvers (smooth bores, good lube, properly dimensioned throats, forcing cones, etc.) and over 1400 fps from rifles.
Recent personal experience with my first S&W revolver in .357 mag found that Remington factory 38 special ammo with soft, swaged LRN bullets did not lead at all, nor did Remington HBWC (another swaged bullet) at 800 or so FPS. Speer 158 grain swaged SWC at 900+ fps also did not lead. However factory remanufactured 38 Special ammo with hard cast LSWs leaded quite abundantly in forcing cone and first cm of bore.
I have yet to take time to slug chamber throats, forcing cone and bore. I may do so in process of shooting Remington SWC 158 grain swaged bullets to velocities of 1100 fps or more -- especially if I encounter more than neglidgeable leading.
Niklas
In cases of revolvers and rifles where bullets are too small, I put soft fiber wads under bullets to stop blowby of powder gasses, which greatly reduces or stops leading.
