BC3/DXT5 ended up working for me. Thanks for the help!

Hi, I've been trying to create a custom crosshair using GIMP 2.8 + DDS 2.1.0 plugin, but when I try it out in-game, I just get a black square where the crosshair should be. I'm pretty sure the problem has to do with me exporting incorrectly--I tried opening with GIMP and exporting an un-modified cro...