I also have the Redding Titanium Carbide die. It sizes the brass down to about .418". The carbide part of my die has a shiny mirror finish and a fairly generous radius on it.
I do remember someone having a similar issue with the sizing rings on his brass a while back. I'll see if I can locate the thread. His problem was that he was trying to get full power loads using a powder that was just too fast for the application, so the brass was flowing outward at the case head a bit too much. When the sizer got to the case head, it left a similar ring. It doesn't seem like that is your problem if the largest diameter at your case heads measures .425"
Originally Posted by Taterhead
Do you mean 0.434"? After firing a hot load?
I'm definitely in the minority here on how I determine pressure limits from fired brass measurements. I know most people measure the case expansion along the thin walls of the case, and that does have some merit. The reason I don't measure there is that part of the brass is constrained by the chamber when it expands, and there is almost always a little bit of spring-back after the pressure drops. So the expansion there approaches a diminishing number as you approach maximum pressure. Instead, I measure expansion at the case head, which is around the thick part of the brass web just above the extraction groove. Even though the expansion there is not as large on a moderately loaded round, the brass isn't constrained by the chamber there, so it is free to increase as the pressure goes up. You get a much more linear measurement, especially at max loadings. I also only measure the first loading with Starline brass. After the first firing, you don't really know what the starting dimension of the case head was, and the brass will start work hardening more after each firing.
I'm not saying one method is right and the other is wrong, I just have found that for me, measuring at the case head gives me what I feel is more useful data.