I had this in another forum, but maybe it is better placed here. I was not sure what I had in FSU lenses, so I checked things out.
Brian,
My J-3 is from 1956 and not 1955 and it is not from KMZ. My J-8 is made in 1955 though.
I weighed all my FSU & CZJ 50mm lenses on a postal scale. There may be room for some error, but it is an OK scale.
Menopta Contax mount 53mm : 160gm
I-50 rigid LTM 59XX : 115gm
Helios 103 Contax mount 81xx : 155gm
Sonnar CZJ 5cm 1.5 LTM 203XX : 220gm
Sonnar CZJ Contax mount 5cm 2.0 collapsible: 165gm
Sonnar CZJ Contax mount 5cm 2.0 198xx: 175gm
Sonnar CZJ Contax mount 5cm 2.0 310xx : 145 gm
J-8 LTM black :130gm
J-8 LTM 55xx : 133gm
J-8M Contax mount : 133 gm.
I-61 LTM 52/2.8 67xxx: 135 gm
I-61 LTM 52/2.8 69xx: 135 gm
I-61 LD Contax mount 55/2.8 95xx: 107gm
Sonnar LTM 5cm 2.0 CZJ 223xxx:185gm
Tessar 50/2.8 LTM CZJ : 165 gm
J-3 Contax mount 56xxx :145gm
Zeiss Opton Contax mount 50/1.5 : 175 gm
Zeiss Opton Contax mount 50/1.5 : 175 gm
J-3 Contax mount 60xxx : 140 gm
I removed any lens covers.