The 84 Illum!!! Yes, I was thinking 81mm. The 84 had an illum rd but we never had it. Yes, that's what it is...I don't know what the back end will look like, it goes into one of those black casings. You do have one? Yes, the Carl Gustav...is rifled. Black aluminum casing...I doubt there was anything at the back but maybe a cap. Looks like this...