The Magtech brass with CBC on the headstamp is what I am using. It works fine for me, but I have reduced the diameter of my expanding plug to eliminate the loose bullet fit problem. I previously encountered the problem with Remington and some other types of brass, so the plug reduction was done long ago. I never noticed the problem with CBC brass because the cure preceeded the Magtech brass.
A tight bullet fit is a good idea, and many expanding plugs are too large. I chuck them in a drill and run the expander against sandpaper until the plug is small enough that loaded rounds have a slight hourglass shape. This completely prevents setback and seems to have no effect on accuracy one way or the other.
This is particularly helpful with some Dillon "powder drop" expander plugs. On rounds that have been roll crimped, the Dillon plug can hang up on the case mouth momentarily. When it then drives on into the case, the powder measure is jolted and has on occasion (in .38 Special) thrown a slight overcharge of powder. Reducing the plug diameter a bit solves this problem.