Can you tell me your source for this? I received this comment on my own forum:
[quote]Swiss authors Christian Reinhart and Michael am Rhyn in their book Automatwaffen II (Dietikon-Zürich 1983) give the rim diameter for the 6.45 mm x 48 GP80 as well as the 5.56 mm x 48 Eiger as 11.9 mm.
Bullet weight for the 6.45 mm (real diameter) was 6.3 g and muzzle velocity 900 m/s from the [experimental] rifle…
Reinhart/am Rhyn explicitly say bullet diameter 6.45 mm (p. 180). They correctly list 7.8 mm for the GP11 and 12.96 mm for the .50BMG. So I think this value is quite reliable.