I put the Hornady blue "single round" followers in my Sig mags. Had to shave them down and disassemble the sig mag to get them in from the bottom on top of the .223 black follower. I describe (roughly) what I did in a related thread - viewtopic.php?f=2&t=4175#p16004 - with a photo.
This reduced the capacity from 12 to 11, but the last round feeds correctly, at least when I manually unload them. I haven't range tested them yet.