I was only interested in the first 50 issues of the series that began in 1986. After #50, the original writers leave, and the book sort of marks time between several writers before finally getting cancelled 7 issues later as part of the Armageddon 2001 revelation mess.
When I started, I was looking at the Janus Directive crossover that concludes in #30 as a breakpoint. It soon became obvious that I did not need to include the rest of the issues of that crossover for Captain Atom. I still kept a breakpoint there, so if I do make a Janus Directive book, it can go there. Originally, I had this planned as three volumes, but condensed it down to two during prep, as I was able to remove a lot of ad pages. The “original” volume 3 became volume 2, and the break between the first two volumes was after Captain Atom #13. The final page of #29 makes for a good dramatic endpoint to a volume. I also opted against adding any extra Invasion! material, which would go around #23-25.
Volume 1
Captain Atom #1-12
Captain Atom Annual #1
Captain Atom #13-22
Captain Atom Annual #2
Captain Atom #23-29
Volume 2
Captain Atom #30-50