3kg.They were 3kg, which was 10% heavier than the issued Sterling Sub Machine Gun (stormtroopers gun) was and about the same as a modern US M4A1 Rifle weighs!
The one I got issued was washed numerous times by both myself, the military and even dry cleaners and it still, to the day I handed it back, stunk of peanut butter when you opened it - a truly hateful bit of kit! I don't have the picture of this any more but when I moved to a Harrier Sqn in the mid 90's I was issued a "short-back" 90L bergen and just the 58 sleeping bag took up the entire bottom third!
My knees just shook thinking about it!