I have found the dimensions. They are as follows:

Overall length not including thread 620mm LG
D- Dia 28.2mm
C- Dia 22mm
D- 24.5mm LG
B- 13.5mm LG
Muzzle Dia 15mm

I found the muzzle diameter to large and therefore the barrel profile to heavy but it is an original Rigby.

Hope this helps or is at least of some interests.

Matt.