The bullet needs to match the throats. The throats need to be at least as big as the groove diameter in your gun (Often called the bore). It should really be .001 to .0015 over the groove diameter.
If the throats are under groove diameter, your pistol will lead no matter what you do because the bullets are sized by the throats and are now undersized for you barrel. Not real common, but does happen, especially if makers are trying to set the gun up for jacketed.
If you sized the loaded round with the sizer, which you haven't answered yet, they would be terribly undersized. If you mean you post sized them with an FCD, it would be less harmful to the bullets, but could still cause undersized bullets which would then lead no matter what.
I am assuming .38 Spl, and it should be easy enough to find a load that does not lead, assuming your barrel is .357 or .358 at most, your throats are over that by .001, your bullets start at .358 or .359, and you are not sizing them down after seating reducing the diameter.
Enough pressure to bump them up to seal the throats and barrel is another requirement unless your barrel, throats, bullets, and bullet hardness are a perfect match.