They CP and Rap4 tips are NOT interchangeable, but I can't help on what threading the Commando barrel is.
Empire Trracer: Custom on/off bottomline
Tippmann SL-68 II: J&J Ceramic
Tippmann TiPX: Voided Warranty, BK Bolt, Remote line
DP Rev-I: TechT L7 Bolt Engine, Dye Hyper 3 reg
PE Geo+: GR2, GST, Violent Series trigger
Ninja Straightline Remote