Cast bullets have to fit to get good accuracy. Jacketed bullets don't require such a fit; they are far more forgiving. Leading is usually caused by an undersized bullet and/ or wrong alloy for the pressure/velocity level. A .429" bullet is generally too small unless you happen to find just the right pressure that causes bullet obturation (bump up, swell up, etc.) so that it fits the bore. If you're using a hard bullet that may not happen.

I've found a soft or maybe wheelweight alloy bullet of .431" (or sometimes even .432") works well for most .44 Special and some .44 Magnum loads. If everything is right, you'll get minimal to no leading. I don't use commercial cast bullets but there are probably plenty on this forum that do and can provide better advice regarding their use.

Some blame lubricants as a cause for leading. Commercial lubricants are too hard, but seldom a serious culprit. Done right, cast bullets are at least as accurate as the best shooting jacketed bullets, but discovering that is often a quest. Good luck-