I have been shooting Hi-Tek coated bullets from Missouri Bullet Co. for awhile now, in .38, .357 & .44 Special and Magnum. I will occasionally pick up a bullet and measure it. All have measured the correct diameter, whether .44 or .357.
I have been buying the 12 Brinnell for target loads and 18 for use in magnum loads. Recently, I read a comment that the old "hard cast" loads used were not really as hard as the 18s. So I have loaded some magnum .357s with 13.5 grains of 2400 with the 12 Brinnell bullets. From the few that I have fired, I don't think I really need the harder rated bullets. Will have to do some more shooting to find out.
I have a feeling that they are not quite as accurate at 25 yards and out as lead bullets, but from my shooting, I can't really prove it. It could be loading technique or differences in shooting from day to day or target to target.
I would like to see a real research project done with ransom rest and different guns and loads to really determine the difference, if any. But, I really like the clean loading, clean shooting characteristics of coated bullets.