Forster - .490 diameter, .498 height
Redding - .500 diameter, .375 height
A Redding does NOT fit in my Forster die.
A Forster will go into a Redding die, but I'm not gonna try it. There's differences in chamfer and stuff, too, that I can't express in measurements.
Sorry for Necro-posting, but I figure out could help somebody out later who's searching for this info.